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 $128.93   12.293%   $144.7794   $144.78   $144.80   $144.80  
  Purchase #2 $189.94   8.107%   $205.3384   $205.34   $205.35   $205.30  
  Purchase #3 $246.69   4.721%   $258.3362   $258.34   $258.35   $258.30  
  Purchase #4 $27.40   8.541%   $29.7402   $29.74   $29.75   $29.70  
  Purchase #5 $210.96   12.525%   $237.3827   $237.38   $237.40   $237.40  
  Purchase #6 $101.95   13.738%   $115.9559   $115.96   $115.95   $116.00  
  Purchase #7 $144.86   13.258%   $164.0655   $164.07   $164.05   $164.10  
  7 purchase totals = $1,050.73       $1,155.5983   $1,155.61   $1,155.65   $1,155.60