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 $61.69   11.197%   $68.5974   $68.60   $68.60   $68.60  
  Purchase #2 $111.39   12.627%   $125.4552   $125.46   $125.45   $125.50  
  Purchase #3 $243.55   6.419%   $259.1835   $259.18   $259.20   $259.20  
  Purchase #4 $36.79   9.838%   $40.4094   $40.41   $40.40   $40.40  
  Purchase #5 $93.98   6.355%   $99.9524   $99.95   $99.95   $100.00  
  Purchase #6 $231.52   6.661%   $246.9415   $246.94   $246.95   $246.90  
  Purchase #7 $57.47   7.572%   $61.8216   $61.82   $61.80   $61.80  
  7 purchase totals = $836.39       $902.3610   $902.36   $902.35   $902.40