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 $60.73   7.150%   $65.0722   $65.07   $65.05   $65.10  
  Purchase #2 $85.41   8.870%   $92.9859   $92.99   $93.00   $93.00  
  Purchase #3 $8.38   13.708%   $9.5287   $9.53   $9.55   $9.50  
  Purchase #4 $206.51   9.277%   $225.6679   $225.67   $225.65   $225.70  
  Purchase #5 $135.75   12.711%   $153.0052   $153.01   $153.00   $153.00  
  Purchase #6 $65.63   4.406%   $68.5217   $68.52   $68.50   $68.50  
  Purchase #7 $144.34   7.102%   $154.591   $154.59   $154.60   $154.60  
  7 purchase totals = $706.75       $769.3726   $769.38   $769.35   $769.40