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 $46.83   12.838%   $52.842   $52.84   $52.85   $52.80  
  Purchase #2 $220.49   4.688%   $230.8266   $230.83   $230.85   $230.80  
  Purchase #3 $119.97   6.354%   $127.5929   $127.59   $127.60   $127.60  
  Purchase #4 $245.58   12.379%   $275.9803   $275.98   $276.00   $276.00  
  Purchase #5 $7.29   10.223%   $8.0353   $8.04   $8.05   $8.00  
  Purchase #6 $169.70   12.304%   $190.5799   $190.58   $190.60   $190.60  
  Purchase #7 $24.76   9.811%   $27.1892   $27.19   $27.20   $27.20  
  7 purchase totals = $834.62       $913.0462   $913.05   $913.15   $913.00