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 $112.69   12.276%   $126.5238   $126.52   $126.50   $126.50  
  Purchase #2 $59.25   10.194%   $65.2899   $65.29   $65.30   $65.30  
  Purchase #3 $182.42   7.822%   $196.6889   $196.69   $196.70   $196.70  
  Purchase #4 $8.66   9.775%   $9.5065   $9.51   $9.50   $9.50  
  Purchase #5 $204.43   11.571%   $228.0846   $228.08   $228.10   $228.10  
  Purchase #6 $158.31   7.705%   $170.5078   $170.51   $170.50   $170.50  
  Purchase #7 $198.73   9.193%   $216.9992   $217.00   $217.00   $217.00  
  7 purchase totals = $924.49       $1,013.6007   $1,013.60   $1,013.60   $1,013.60