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 $92.51   12.341%   $103.9267   $103.93   $103.95   $103.90  
  Purchase #2 $203.67   7.482%   $218.9086   $218.91   $218.90   $218.90  
  Purchase #3 $91.25   12.525%   $102.6791   $102.68   $102.70   $102.70  
  Purchase #4 $135.80   12.441%   $152.6949   $152.69   $152.70   $152.70  
  Purchase #5 $149.84   12.733%   $168.9191   $168.92   $168.90   $168.90  
  Purchase #6 $196.56   3.590%   $203.6165   $203.62   $203.60   $203.60  
  Purchase #7 $72.29   13.345%   $81.9371   $81.94   $81.95   $81.90  
  7 purchase totals = $941.92       $1,032.6820   $1,032.69   $1,032.70   $1,032.60