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 $85.80   9.102%   $93.6095   $93.61   $93.60   $93.60  
  Purchase #2 $32.77   4.769%   $34.3328   $34.33   $34.35   $34.30  
  Purchase #3 $223.56   6.225%   $237.4766   $237.48   $237.50   $237.50  
  Purchase #4 $184.91   7.706%   $199.1592   $199.16   $199.15   $199.20  
  Purchase #5 $218.34   12.489%   $245.6085   $245.61   $245.60   $245.60  
  Purchase #6 $142.68   11.478%   $159.0568   $159.06   $159.05   $159.10  
  Purchase #7 $160.36   6.466%   $170.7289   $170.73   $170.75   $170.70  
  7 purchase totals = $1,048.42       $1,139.9723   $1,139.98   $1,140.00   $1,140.00