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 $58.86   13.238%   $66.6519   $66.65   $66.65   $66.70  
  Purchase #2 $133.45   5.837%   $141.2395   $141.24   $141.25   $141.20  
  Purchase #3 $105.88   8.283%   $114.65   $114.65   $114.65   $114.70  
  Purchase #4 $59.67   13.470%   $67.7075   $67.71   $67.70   $67.70  
  Purchase #5 $230.58   4.196%   $240.2551   $240.26   $240.25   $240.30  
  Purchase #6 $19.57   13.259%   $22.1648   $22.16   $22.15   $22.20  
  Purchase #7 $133.42   12.778%   $150.4684   $150.47   $150.45   $150.50  
  7 purchase totals = $741.43       $803.1372   $803.14   $803.10   $803.30