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 $68.99   4.594%   $72.1594   $72.16   $72.15   $72.20  
  Purchase #2 $243.90   8.217%   $263.9413   $263.94   $263.95   $263.90  
  Purchase #3 $102.52   3.416%   $106.0221   $106.02   $106.00   $106.00  
  Purchase #4 $170.79   3.533%   $176.824   $176.82   $176.80   $176.80  
  Purchase #5 $137.90   10.416%   $152.2637   $152.26   $152.25   $152.30  
  Purchase #6 $193.39   10.277%   $213.2647   $213.26   $213.25   $213.30  
  Purchase #7 $64.80   11.694%   $72.3777   $72.38   $72.40   $72.40  
  7 purchase totals = $982.29       $1,056.8529   $1,056.84   $1,056.80   $1,056.90