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 $58.87   8.662%   $63.9693   $63.97   $63.95   $64.00  
  Purchase #2 $232.79   9.164%   $254.1229   $254.12   $254.10   $254.10  
  Purchase #3 $92.33   12.373%   $103.754   $103.75   $103.75   $103.80  
  Purchase #4 $29.65   11.570%   $33.0805   $33.08   $33.10   $33.10  
  Purchase #5 $123.91   6.850%   $132.3978   $132.40   $132.40   $132.40  
  Purchase #6 $163.51   4.139%   $170.2777   $170.28   $170.30   $170.30  
  Purchase #7 $91.35   6.631%   $97.4074   $97.41   $97.40   $97.40  
  7 purchase totals = $792.41       $855.0096   $855.01   $855.00   $855.10