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 $55.44   13.594%   $62.9765   $62.98   $63.00   $63.00  
  Purchase #2 $193.99   9.762%   $212.9273   $212.93   $212.95   $212.90  
  Purchase #3 $119.55   8.452%   $129.6544   $129.65   $129.65   $129.70  
  Purchase #4 $171.45   10.669%   $189.742   $189.74   $189.75   $189.70  
  Purchase #5 $250.97   7.437%   $269.6346   $269.63   $269.65   $269.60  
  Purchase #6 $142.35   12.225%   $159.7523   $159.75   $159.75   $159.80  
  Purchase #7 $125.93   4.706%   $131.8563   $131.86   $131.85   $131.90  
  7 purchase totals = $1,059.68       $1,156.5434   $1,156.54   $1,156.60   $1,156.60