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 $25.46   3.476%   $26.345   $26.35   $26.35   $26.30  
  Purchase #2 $223.99   7.799%   $241.459   $241.46   $241.45   $241.50  
  Purchase #3 $60.62   4.241%   $63.1909   $63.19   $63.20   $63.20  
  Purchase #4 $86.61   9.457%   $94.8007   $94.80   $94.80   $94.80  
  Purchase #5 $57.41   8.725%   $62.419   $62.42   $62.40   $62.40  
  Purchase #6 $10.34   9.188%   $11.29   $11.29   $11.30   $11.30  
  Purchase #7 $120.95   6.208%   $128.4586   $128.46   $128.45   $128.50  
  7 purchase totals = $585.38       $627.9632   $627.97   $627.95   $628.00