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 $62.52   3.206%   $64.5244   $64.52   $64.50   $64.50  
  Purchase #2 $65.43   3.736%   $67.8745   $67.87   $67.85   $67.90  
  Purchase #3 $200.32   13.286%   $226.9345   $226.93   $226.95   $226.90  
  Purchase #4 $66.34   3.819%   $68.8735   $68.87   $68.85   $68.90  
  Purchase #5 $128.79   5.769%   $136.2199   $136.22   $136.20   $136.20  
  Purchase #6 $177.61   3.155%   $183.2136   $183.21   $183.20   $183.20  
  Purchase #7 $23.66   11.114%   $26.2896   $26.29   $26.30   $26.30  
  7 purchase totals = $724.67       $773.9300   $773.91   $773.85   $773.90