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 $207.33   8.821%   $225.6186   $225.62   $225.60   $225.60  
  Purchase #2 $57.45   13.646%   $65.2896   $65.29   $65.30   $65.30  
  Purchase #3 $144.80   11.440%   $161.3651   $161.37   $161.35   $161.40  
  Purchase #4 $144.86   4.191%   $150.9311   $150.93   $150.95   $150.90  
  Purchase #5 $122.85   7.180%   $131.6706   $131.67   $131.65   $131.70  
  Purchase #6 $249.36   6.437%   $265.4113   $265.41   $265.40   $265.40  
  Purchase #7 $22.62   7.584%   $24.3355   $24.34   $24.35   $24.30  
  7 purchase totals = $949.27       $1,024.6218   $1,024.63   $1,024.60   $1,024.60