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 $178.48   3.658%   $185.0088   $185.01   $185.00   $185.00  
  Purchase #2 $219.29   13.661%   $249.2472   $249.25   $249.25   $249.20  
  Purchase #3 $201.93   8.629%   $219.3545   $219.35   $219.35   $219.40  
  Purchase #4 $46.35   11.761%   $51.8012   $51.80   $51.80   $51.80  
  Purchase #5 $189.85   6.794%   $202.7484   $202.75   $202.75   $202.70  
  Purchase #6 $200.50   11.172%   $222.8999   $222.90   $222.90   $222.90  
  Purchase #7 $120.89   3.615%   $125.2602   $125.26   $125.25   $125.30  
  7 purchase totals = $1,157.29       $1,256.3202   $1,256.32   $1,256.30   $1,256.30