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 $232.36   11.473%   $259.0187   $259.02   $259.00   $259.00  
  Purchase #2 $90.50   10.109%   $99.6486   $99.65   $99.65   $99.60  
  Purchase #3 $224.72   5.614%   $237.3358   $237.34   $237.35   $237.30  
  Purchase #4 $62.96   3.244%   $65.0024   $65.00   $65.00   $65.00  
  Purchase #5 $31.55   11.354%   $35.1322   $35.13   $35.15   $35.10  
  Purchase #6 $228.28   6.104%   $242.2142   $242.21   $242.20   $242.20  
  Purchase #7 $42.32   10.195%   $46.6345   $46.63   $46.65   $46.60  
  7 purchase totals = $912.69       $984.9864   $984.98   $985.00   $984.80