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 $189.49   9.234%   $206.9875   $206.99   $207.00   $207.00  
  Purchase #2 $249.42   6.792%   $266.3606   $266.36   $266.35   $266.40  
  Purchase #3 $68.41   4.110%   $71.2217   $71.22   $71.20   $71.20  
  Purchase #4 $200.94   7.649%   $216.3099   $216.31   $216.30   $216.30  
  Purchase #5 $172.80   10.750%   $191.376   $191.38   $191.40   $191.40  
  Purchase #6 $250.76   12.354%   $281.7389   $281.74   $281.75   $281.70  
  Purchase #7 $115.29   4.617%   $120.6129   $120.61   $120.60   $120.60  
  7 purchase totals = $1,247.11       $1,354.6075   $1,354.61   $1,354.60   $1,354.60