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 $148.29   13.327%   $168.0526   $168.05   $168.05   $168.10  
  Purchase #2 $151.75   11.836%   $169.7111   $169.71   $169.70   $169.70  
  Purchase #3 $59.35   5.735%   $62.7537   $62.75   $62.75   $62.80  
  Purchase #4 $93.32   5.513%   $98.4647   $98.46   $98.45   $98.50  
  Purchase #5 $210.64   9.559%   $230.7751   $230.78   $230.80   $230.80  
  Purchase #6 $169.73   6.443%   $180.6657   $180.67   $180.65   $180.70  
  Purchase #7 $200.56   12.350%   $225.3292   $225.33   $225.35   $225.30  
  7 purchase totals = $1,033.64       $1,135.7521   $1,135.75   $1,135.75   $1,135.90