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 $110.48   13.441%   $125.3296   $125.33   $125.35   $125.30  
  Purchase #2 $245.92   9.672%   $269.7054   $269.71   $269.70   $269.70  
  Purchase #3 $113.85   5.514%   $120.1277   $120.13   $120.15   $120.10  
  Purchase #4 $192.35   6.723%   $205.2817   $205.28   $205.30   $205.30  
  Purchase #5 $198.57   13.257%   $224.8944   $224.89   $224.90   $224.90  
  Purchase #6 $97.37   7.632%   $104.8013   $104.80   $104.80   $104.80  
  Purchase #7 $33.89   9.753%   $37.1953   $37.20   $37.20   $37.20  
  7 purchase totals = $992.43       $1,087.3354   $1,087.34   $1,087.40   $1,087.30