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 $126.31   6.330%   $134.3054   $134.31   $134.30   $134.30  
  Purchase #2 $226.67   13.165%   $256.5111   $256.51   $256.50   $256.50  
  Purchase #3 $94.37   5.694%   $99.7434   $99.74   $99.75   $99.70  
  Purchase #4 $177.29   11.446%   $197.5826   $197.58   $197.60   $197.60  
  Purchase #5 $126.32   8.498%   $137.0547   $137.05   $137.05   $137.10  
  Purchase #6 $210.99   8.299%   $228.5001   $228.50   $228.50   $228.50  
  Purchase #7 $196.34   5.672%   $207.4764   $207.48   $207.50   $207.50  
  7 purchase totals = $1,158.29       $1,261.1737   $1,261.17   $1,261.20   $1,261.20