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 $204.61   9.632%   $224.318   $224.32   $224.30   $224.30  
  Purchase #2 $181.43   6.448%   $193.1286   $193.13   $193.15   $193.10  
  Purchase #3 $202.28   12.780%   $228.1314   $228.13   $228.15   $228.10  
  Purchase #4 $168.74   12.590%   $189.9844   $189.98   $190.00   $190.00  
  Purchase #5 $31.49   5.657%   $33.2714   $33.27   $33.25   $33.30  
  Purchase #6 $119.61   5.183%   $125.8094   $125.81   $125.80   $125.80  
  Purchase #7 $239.43   12.339%   $268.9733   $268.97   $268.95   $269.00  
  7 purchase totals = $1,147.59       $1,263.6165   $1,263.61   $1,263.60   $1,263.60