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 $236.51   9.547%   $259.0896   $259.09   $259.10   $259.10  
  Purchase #2 $60.31   5.678%   $63.7344   $63.73   $63.75   $63.70  
  Purchase #3 $105.35   9.496%   $115.354   $115.35   $115.35   $115.40  
  Purchase #4 $196.79   13.698%   $223.7463   $223.75   $223.75   $223.70  
  Purchase #5 $161.53   6.561%   $172.128   $172.13   $172.15   $172.10  
  Purchase #6 $79.73   5.366%   $84.0083   $84.01   $84.00   $84.00  
  Purchase #7 $116.38   7.595%   $125.2191   $125.22   $125.20   $125.20  
  7 purchase totals = $956.60       $1,043.2797   $1,043.28   $1,043.30   $1,043.20