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 $241.69   12.255%   $271.3091   $271.31   $271.30   $271.30  
  Purchase #2 $120.72   10.748%   $133.695   $133.70   $133.70   $133.70  
  Purchase #3 $44.70   3.339%   $46.1925   $46.19   $46.20   $46.20  
  Purchase #4 $150.94   7.175%   $161.7699   $161.77   $161.75   $161.80  
  Purchase #5 $171.25   9.606%   $187.7003   $187.70   $187.70   $187.70  
  Purchase #6 $56.38   12.479%   $63.4157   $63.42   $63.40   $63.40  
  Purchase #7 $152.75   11.729%   $170.666   $170.67   $170.65   $170.70  
  7 purchase totals = $938.43       $1,034.7485   $1,034.76   $1,034.70   $1,034.80