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 $210.76   11.288%   $234.5506   $234.55   $234.55   $234.60  
  Purchase #2 $91.77   12.678%   $103.4046   $103.40   $103.40   $103.40  
  Purchase #3 $113.42   10.582%   $125.4221   $125.42   $125.40   $125.40  
  Purchase #4 $191.66   5.422%   $202.0518   $202.05   $202.05   $202.10  
  Purchase #5 $115.85   10.652%   $128.1903   $128.19   $128.20   $128.20  
  Purchase #6 $69.84   8.752%   $75.9524   $75.95   $75.95   $76.00  
  Purchase #7 $174.60   8.774%   $189.9194   $189.92   $189.90   $189.90  
  7 purchase totals = $967.90       $1,059.4912   $1,059.48   $1,059.45   $1,059.60