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 $240.34   9.403%   $262.9392   $262.94   $262.95   $262.90  
  Purchase #2 $183.69   9.672%   $201.4565   $201.46   $201.45   $201.50  
  Purchase #3 $129.53   4.306%   $135.1076   $135.11   $135.10   $135.10  
  Purchase #4 $245.71   13.708%   $279.3919   $279.39   $279.40   $279.40  
  Purchase #5 $249.49   6.873%   $266.6374   $266.64   $266.65   $266.60  
  Purchase #6 $179.85   3.183%   $185.5746   $185.57   $185.55   $185.60  
  Purchase #7 $22.56   3.741%   $23.404   $23.40   $23.40   $23.40  
  7 purchase totals = $1,251.17       $1,354.5112   $1,354.51   $1,354.50   $1,354.50