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 $64.48   10.662%   $71.3549   $71.35   $71.35   $71.40  
  Purchase #2 $94.86   11.279%   $105.5593   $105.56   $105.55   $105.60  
  Purchase #3 $17.66   11.422%   $19.6771   $19.68   $19.70   $19.70  
  Purchase #4 $211.29   5.286%   $222.4588   $222.46   $222.45   $222.50  
  Purchase #5 $201.86   9.211%   $220.4533   $220.45   $220.45   $220.50  
  Purchase #6 $98.71   7.729%   $106.3393   $106.34   $106.35   $106.30  
  Purchase #7 $239.76   8.699%   $260.6167   $260.62   $260.60   $260.60  
  7 purchase totals = $928.62       $1,006.4594   $1,006.46   $1,006.45   $1,006.60