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 $68.89   11.843%   $77.0486   $77.05   $77.05   $77.00  
  Purchase #2 $102.33   4.218%   $106.6463   $106.65   $106.65   $106.60  
  Purchase #3 $12.43   10.714%   $13.7618   $13.76   $13.75   $13.80  
  Purchase #4 $42.31   4.666%   $44.2842   $44.28   $44.30   $44.30  
  Purchase #5 $43.49   5.595%   $45.9233   $45.92   $45.90   $45.90  
  Purchase #6 $229.76   11.513%   $256.2123   $256.21   $256.20   $256.20  
  Purchase #7 $232.46   13.361%   $263.519   $263.52   $263.50   $263.50  
  7 purchase totals = $731.67       $807.3955   $807.39   $807.35   $807.30