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 $68.74   13.343%   $77.912   $77.91   $77.90   $77.90  
  Purchase #2 $26.29   3.457%   $27.1988   $27.20   $27.20   $27.20  
  Purchase #3 $158.70   7.365%   $170.3883   $170.39   $170.40   $170.40  
  Purchase #4 $197.38   3.734%   $204.7502   $204.75   $204.75   $204.80  
  Purchase #5 $249.67   6.127%   $264.9673   $264.97   $264.95   $265.00  
  Purchase #6 $50.44   8.854%   $54.906   $54.91   $54.90   $54.90  
  Purchase #7 $7.59   3.355%   $7.8446   $7.84   $7.85   $7.80  
  7 purchase totals = $758.81       $807.9672   $807.97   $807.95   $808.00