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 $87.98   7.307%   $94.4087   $94.41   $94.40   $94.40  
  Purchase #2 $138.25   4.627%   $144.6468   $144.65   $144.65   $144.60  
  Purchase #3 $114.49   4.815%   $120.0027   $120.00   $120.00   $120.00  
  Purchase #4 $112.30   11.780%   $125.5289   $125.53   $125.55   $125.50  
  Purchase #5 $120.57   5.284%   $126.9409   $126.94   $126.95   $126.90  
  Purchase #6 $196.78   8.802%   $214.1006   $214.10   $214.10   $214.10  
  Purchase #7 $162.37   10.251%   $179.0145   $179.01   $179.00   $179.00  
  7 purchase totals = $932.74       $1,004.6431   $1,004.64   $1,004.65   $1,004.50