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 $57.84   3.751%   $60.0096   $60.01   $60.00   $60.00  
  Purchase #2 $155.79   6.775%   $166.3448   $166.34   $166.35   $166.30  
  Purchase #3 $125.25   9.619%   $137.2978   $137.30   $137.30   $137.30  
  Purchase #4 $103.72   8.264%   $112.2914   $112.29   $112.30   $112.30  
  Purchase #5 $88.52   6.446%   $94.226   $94.23   $94.25   $94.20  
  Purchase #6 $147.28   12.107%   $165.1112   $165.11   $165.10   $165.10  
  Purchase #7 $47.99   6.357%   $51.0407   $51.04   $51.05   $51.00  
  7 purchase totals = $726.39       $786.3215   $786.32   $786.35   $786.20