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 $231.69   10.508%   $256.036   $256.04   $256.05   $256.00  
  Purchase #2 $50.89   5.147%   $53.5093   $53.51   $53.50   $53.50  
  Purchase #3 $216.80   9.445%   $237.2768   $237.28   $237.30   $237.30  
  Purchase #4 $195.86   8.106%   $211.7364   $211.74   $211.75   $211.70  
  Purchase #5 $143.88   12.844%   $162.3599   $162.36   $162.35   $162.40  
  Purchase #6 $161.51   8.249%   $174.833   $174.83   $174.85   $174.80  
  Purchase #7 $65.39   12.474%   $73.5467   $73.55   $73.55   $73.50  
  7 purchase totals = $1,066.02       $1,169.2981   $1,169.31   $1,169.35   $1,169.20