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 $83.42   12.499%   $93.8467   $93.85   $93.85   $93.80  
  Purchase #2 $243.43   13.801%   $277.0258   $277.03   $277.05   $277.00  
  Purchase #3 $125.99   3.501%   $130.4009   $130.40   $130.40   $130.40  
  Purchase #4 $154.95   5.156%   $162.9392   $162.94   $162.95   $162.90  
  Purchase #5 $184.98   13.106%   $209.2235   $209.22   $209.20   $209.20  
  Purchase #6 $85.33   12.699%   $96.1661   $96.17   $96.15   $96.20  
  Purchase #7 $227.42   13.445%   $257.9966   $258.00   $258.00   $258.00  
  7 purchase totals = $1,105.52       $1,227.5988   $1,227.61   $1,227.60   $1,227.50