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 $66.25   10.397%   $73.138   $73.14   $73.15   $73.10  
  Purchase #2 $85.68   4.610%   $89.6298   $89.63   $89.65   $89.60  
  Purchase #3 $62.70   9.183%   $68.4577   $68.46   $68.45   $68.50  
  Purchase #4 $240.55   4.160%   $250.5569   $250.56   $250.55   $250.60  
  Purchase #5 $236.32   9.205%   $258.0733   $258.07   $258.05   $258.10  
  Purchase #6 $242.40   9.429%   $265.2559   $265.26   $265.25   $265.30  
  Purchase #7 $7.94   12.614%   $8.9416   $8.94   $8.95   $8.90  
  7 purchase totals = $941.84       $1,014.0532   $1,014.06   $1,014.05   $1,014.10