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 $30.63   13.458%   $34.7522   $34.75   $34.75   $34.80  
  Purchase #2 $238.25   4.534%   $249.0523   $249.05   $249.05   $249.10  
  Purchase #3 $151.43   13.445%   $171.7898   $171.79   $171.80   $171.80  
  Purchase #4 $128.61   7.359%   $138.0744   $138.07   $138.05   $138.10  
  Purchase #5 $203.99   6.794%   $217.8491   $217.85   $217.85   $217.80  
  Purchase #6 $197.77   9.686%   $216.926   $216.93   $216.95   $216.90  
  Purchase #7 $15.44   7.281%   $16.5642   $16.56   $16.55   $16.60  
  7 purchase totals = $966.12       $1,045.0080   $1,045.00   $1,045.00   $1,045.10