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 $107.46   5.196%   $113.0436   $113.04   $113.05   $113.00  
  Purchase #2 $187.67   6.321%   $199.5326   $199.53   $199.55   $199.50  
  Purchase #3 $68.37   4.145%   $71.2039   $71.20   $71.20   $71.20  
  Purchase #4 $242.79   5.314%   $255.6919   $255.69   $255.70   $255.70  
  Purchase #5 $11.86   9.762%   $13.0178   $13.02   $13.00   $13.00  
  Purchase #6 $238.99   6.843%   $255.3441   $255.34   $255.35   $255.30  
  Purchase #7 $54.36   6.193%   $57.7265   $57.73   $57.75   $57.70  
  7 purchase totals = $911.50       $965.5604   $965.55   $965.60   $965.40