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 $76.93   8.310%   $83.3229   $83.32   $83.30   $83.30  
  Purchase #2 $194.91   11.718%   $217.7496   $217.75   $217.75   $217.70  
  Purchase #3 $144.88   12.413%   $162.864   $162.86   $162.85   $162.90  
  Purchase #4 $129.56   6.169%   $137.5526   $137.55   $137.55   $137.60  
  Purchase #5 $153.70   10.190%   $169.362   $169.36   $169.35   $169.40  
  Purchase #6 $221.39   13.346%   $250.9367   $250.94   $250.95   $250.90  
  Purchase #7 $184.63   5.475%   $194.7385   $194.74   $194.75   $194.70  
  7 purchase totals = $1,106.00       $1,216.5263   $1,216.52   $1,216.50   $1,216.50