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 $236.58   9.298%   $258.5772   $258.58   $258.60   $258.60  
  Purchase #2 $67.84   12.452%   $76.2874   $76.29   $76.30   $76.30  
  Purchase #3 $118.73   3.578%   $122.9782   $122.98   $123.00   $123.00  
  Purchase #4 $223.94   4.446%   $233.8964   $233.90   $233.90   $233.90  
  Purchase #5 $231.74   4.722%   $242.6828   $242.68   $242.70   $242.70  
  Purchase #6 $162.50   6.443%   $172.9699   $172.97   $172.95   $173.00  
  Purchase #7 $17.32   9.825%   $19.0217   $19.02   $19.00   $19.00  
  7 purchase totals = $1,058.65       $1,126.4136   $1,126.42   $1,126.45   $1,126.50