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 $62.58   11.569%   $69.8199   $69.82   $69.80   $69.80  
  Purchase #2 $120.35   5.300%   $126.7286   $126.73   $126.75   $126.70  
  Purchase #3 $189.84   4.329%   $198.0582   $198.06   $198.05   $198.10  
  Purchase #4 $189.57   10.671%   $209.799   $209.80   $209.80   $209.80  
  Purchase #5 $26.50   6.538%   $28.2326   $28.23   $28.25   $28.20  
  Purchase #6 $14.41   6.476%   $15.3432   $15.34   $15.35   $15.30  
  Purchase #7 $178.61   13.848%   $203.3439   $203.34   $203.35   $203.30  
  7 purchase totals = $781.86       $851.3254   $851.32   $851.35   $851.20