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 $118.73   3.179%   $122.5044   $122.50   $122.50   $122.50  
  Purchase #2 $203.87   7.409%   $218.9747   $218.97   $218.95   $219.00  
  Purchase #3 $38.35   11.304%   $42.6851   $42.69   $42.70   $42.70  
  Purchase #4 $140.59   6.840%   $150.2064   $150.21   $150.20   $150.20  
  Purchase #5 $59.55   11.494%   $66.3947   $66.39   $66.40   $66.40  
  Purchase #6 $70.70   8.546%   $76.742   $76.74   $76.75   $76.70  
  Purchase #7 $70.49   11.336%   $78.4807   $78.48   $78.50   $78.50  
  7 purchase totals = $702.28       $755.9880   $755.98   $756.00   $756.00