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 $32.55   3.652%   $33.7387   $33.74   $33.75   $33.70  
  Purchase #2 $171.51   9.248%   $187.3712   $187.37   $187.35   $187.40  
  Purchase #3 $239.90   13.300%   $271.8067   $271.81   $271.80   $271.80  
  Purchase #4 $216.91   13.812%   $246.8696   $246.87   $246.85   $246.90  
  Purchase #5 $118.69   6.826%   $126.7918   $126.79   $126.80   $126.80  
  Purchase #6 $207.82   13.649%   $236.1854   $236.19   $236.20   $236.20  
  Purchase #7 $163.71   3.836%   $169.9899   $169.99   $170.00   $170.00  
  7 purchase totals = $1,151.09       $1,272.7533   $1,272.76   $1,272.75   $1,272.80