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 $23.43   10.867%   $25.9761   $25.98   $26.00   $26.00  
  Purchase #2 $189.89   8.618%   $206.2547   $206.25   $206.25   $206.30  
  Purchase #3 $61.44   6.211%   $65.256   $65.26   $65.25   $65.30  
  Purchase #4 $134.55   10.532%   $148.7208   $148.72   $148.70   $148.70  
  Purchase #5 $69.45   11.628%   $77.5256   $77.53   $77.55   $77.50  
  Purchase #6 $239.68   10.507%   $264.8632   $264.86   $264.85   $264.90  
  Purchase #7 $87.46   5.551%   $92.3149   $92.31   $92.30   $92.30  
  7 purchase totals = $805.90       $880.9113   $880.91   $880.90   $881.00