Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $232.48   8.190%   $251.5201   $251.52   $251.50   $251.50  
  Purchase #2 $113.51   7.285%   $121.7792   $121.78   $121.80   $121.80  
  Purchase #3 $186.96   9.614%   $204.9343   $204.93   $204.95   $204.90  
  Purchase #4 $240.34   4.476%   $251.0976   $251.10   $251.10   $251.10  
  Purchase #5 $155.40   9.712%   $170.4924   $170.49   $170.50   $170.50  
  Purchase #6 $137.91   11.661%   $153.9917   $153.99   $154.00   $154.00  
  Purchase #7 $165.66   9.369%   $181.1807   $181.18   $181.20   $181.20  
  7 purchase totals = $1,232.26       $1,334.9960   $1,334.99   $1,335.05   $1,335.00