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 $194.62   11.838%   $217.6591   $217.66   $217.65   $217.70  
  Purchase #2 $131.82   9.480%   $144.3165   $144.32   $144.30   $144.30  
  Purchase #3 $63.51   12.220%   $71.2709   $71.27   $71.25   $71.30  
  Purchase #4 $181.97   12.185%   $204.143   $204.14   $204.15   $204.10  
  Purchase #5 $6.26   6.714%   $6.6803   $6.68   $6.70   $6.70  
  Purchase #6 $135.34   4.581%   $141.5399   $141.54   $141.55   $141.50  
  Purchase #7 $247.79   8.576%   $269.0405   $269.04   $269.05   $269.00  
  7 purchase totals = $961.31       $1,054.6502   $1,054.65   $1,054.65   $1,054.60