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 $109.48   10.179%   $120.624   $120.62   $120.60   $120.60  
  Purchase #2 $135.61   5.781%   $143.4496   $143.45   $143.45   $143.40  
  Purchase #3 $176.70   11.757%   $197.4746   $197.47   $197.45   $197.50  
  Purchase #4 $178.73   3.387%   $184.7836   $184.78   $184.80   $184.80  
  Purchase #5 $180.26   7.594%   $193.9489   $193.95   $193.95   $193.90  
  Purchase #6 $91.45   12.318%   $102.7148   $102.71   $102.70   $102.70  
  Purchase #7 $73.95   10.653%   $81.8279   $81.83   $81.85   $81.80  
  7 purchase totals = $946.18       $1,024.8234   $1,024.81   $1,024.80   $1,024.70