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 $133.59   9.529%   $146.3198   $146.32   $146.30   $146.30  
  Purchase #2 $217.79   10.127%   $239.8456   $239.85   $239.85   $239.80  
  Purchase #3 $196.94   9.713%   $216.0688   $216.07   $216.05   $216.10  
  Purchase #4 $6.57   5.114%   $6.906   $6.91   $6.90   $6.90  
  Purchase #5 $89.39   3.623%   $92.6286   $92.63   $92.65   $92.60  
  Purchase #6 $74.31   8.327%   $80.4978   $80.50   $80.50   $80.50  
  Purchase #7 $236.63   6.326%   $251.5992   $251.60   $251.60   $251.60  
  7 purchase totals = $955.22       $1,033.8658   $1,033.88   $1,033.85   $1,033.80