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 $57.79   10.687%   $63.966   $63.97   $63.95   $64.00  
  Purchase #2 $15.68   10.322%   $17.2985   $17.30   $17.30   $17.30  
  Purchase #3 $147.75   13.424%   $167.584   $167.58   $167.60   $167.60  
  Purchase #4 $215.54   6.481%   $229.5091   $229.51   $229.50   $229.50  
  Purchase #5 $228.45   4.347%   $238.3807   $238.38   $238.40   $238.40  
  Purchase #6 $41.49   10.592%   $45.8846   $45.88   $45.90   $45.90  
  Purchase #7 $210.44   10.199%   $231.9028   $231.90   $231.90   $231.90  
  7 purchase totals = $917.14       $994.5257   $994.52   $994.55   $994.60