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 $222.40   13.142%   $251.6278   $251.63   $251.65   $251.60  
  Purchase #2 $69.46   4.560%   $72.6274   $72.63   $72.65   $72.60  
  Purchase #3 $163.97   6.128%   $174.0181   $174.02   $174.00   $174.00  
  Purchase #4 $54.91   11.600%   $61.2796   $61.28   $61.30   $61.30  
  Purchase #5 $74.26   11.294%   $82.6469   $82.65   $82.65   $82.60  
  Purchase #6 $222.35   13.751%   $252.9253   $252.93   $252.95   $252.90  
  Purchase #7 $235.34   9.276%   $257.1701   $257.17   $257.15   $257.20  
  7 purchase totals = $1,042.69       $1,152.2952   $1,152.31   $1,152.35   $1,152.20