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 $203.94   10.322%   $224.9907   $224.99   $225.00   $225.00  
  Purchase #2 $210.52   10.469%   $232.5593   $232.56   $232.55   $232.60  
  Purchase #3 $75.42   3.714%   $78.2211   $78.22   $78.20   $78.20  
  Purchase #4 $203.30   8.605%   $220.794   $220.79   $220.80   $220.80  
  Purchase #5 $87.55   4.639%   $91.6114   $91.61   $91.60   $91.60  
  Purchase #6 $50.25   6.514%   $53.5233   $53.52   $53.50   $53.50  
  Purchase #7 $204.90   6.181%   $217.5649   $217.56   $217.55   $217.60  
  7 purchase totals = $1,035.88       $1,119.2647   $1,119.25   $1,119.20   $1,119.30