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 $114.41   4.846%   $119.9543   $119.95   $119.95   $120.00  
  Purchase #2 $198.30   13.777%   $225.6198   $225.62   $225.60   $225.60  
  Purchase #3 $235.30   12.492%   $264.6937   $264.69   $264.70   $264.70  
  Purchase #4 $150.43   6.761%   $160.6006   $160.60   $160.60   $160.60  
  Purchase #5 $33.65   8.232%   $36.4201   $36.42   $36.40   $36.40  
  Purchase #6 $83.34   9.374%   $91.1523   $91.15   $91.15   $91.20  
  Purchase #7 $250.93   7.486%   $269.7146   $269.71   $269.70   $269.70  
  7 purchase totals = $1,066.36       $1,168.1554   $1,168.14   $1,168.10   $1,168.20