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 $196.94   6.271%   $209.2901   $209.29   $209.30   $209.30  
  Purchase #2 $181.65   10.755%   $201.1865   $201.19   $201.20   $201.20  
  Purchase #3 $152.38   5.820%   $161.2485   $161.25   $161.25   $161.20  
  Purchase #4 $121.33   10.321%   $133.8525   $133.85   $133.85   $133.90  
  Purchase #5 $158.57   7.744%   $170.8497   $170.85   $170.85   $170.80  
  Purchase #6 $64.88   12.711%   $73.1269   $73.13   $73.15   $73.10  
  Purchase #7 $48.78   11.203%   $54.2448   $54.24   $54.25   $54.20  
  7 purchase totals = $924.53       $1,003.7990   $1,003.80   $1,003.85   $1,003.70