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 $59.58   13.605%   $67.6859   $67.69   $67.70   $67.70  
  Purchase #2 $250.77   13.664%   $285.0352   $285.04   $285.05   $285.00  
  Purchase #3 $215.35   6.840%   $230.0799   $230.08   $230.10   $230.10  
  Purchase #4 $127.68   4.735%   $133.7256   $133.73   $133.75   $133.70  
  Purchase #5 $236.87   11.221%   $263.4492   $263.45   $263.45   $263.40  
  Purchase #6 $53.66   6.645%   $57.2257   $57.23   $57.25   $57.20  
  Purchase #7 $148.26   3.591%   $153.584   $153.58   $153.60   $153.60  
  7 purchase totals = $1,092.17       $1,190.7855   $1,190.80   $1,190.90   $1,190.70