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 $41.92   3.694%   $43.4685   $43.47   $43.45   $43.50  
  Purchase #2 $216.47   7.233%   $232.1273   $232.13   $232.15   $232.10  
  Purchase #3 $231.36   8.279%   $250.5143   $250.51   $250.50   $250.50  
  Purchase #4 $184.65   13.489%   $209.5574   $209.56   $209.55   $209.60  
  Purchase #5 $234.57   13.452%   $266.1244   $266.12   $266.10   $266.10  
  Purchase #6 $24.67   6.137%   $26.184   $26.18   $26.20   $26.20  
  Purchase #7 $236.60   8.174%   $255.9397   $255.94   $255.95   $255.90  
  7 purchase totals = $1,170.24       $1,283.9156   $1,283.91   $1,283.90   $1,283.90