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 $37.58   8.450%   $40.7555   $40.76   $40.75   $40.80  
  Purchase #2 $232.28   5.419%   $244.8673   $244.87   $244.85   $244.90  
  Purchase #3 $63.98   6.744%   $68.2948   $68.29   $68.30   $68.30  
  Purchase #4 $102.58   4.201%   $106.8894   $106.89   $106.90   $106.90  
  Purchase #5 $248.47   13.173%   $281.201   $281.20   $281.20   $281.20  
  Purchase #6 $213.54   10.530%   $236.0258   $236.03   $236.05   $236.00  
  Purchase #7 $79.56   6.428%   $84.6741   $84.67   $84.65   $84.70  
  7 purchase totals = $977.99       $1,062.7079   $1,062.71   $1,062.70   $1,062.80