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 $146.45   11.606%   $163.447   $163.45   $163.45   $163.40  
  Purchase #2 $87.81   10.327%   $96.8781   $96.88   $96.90   $96.90  
  Purchase #3 $119.39   10.243%   $131.6191   $131.62   $131.60   $131.60  
  Purchase #4 $236.48   7.471%   $254.1474   $254.15   $254.15   $254.10  
  Purchase #5 $131.63   11.574%   $146.8649   $146.86   $146.85   $146.90  
  Purchase #6 $21.94   9.386%   $23.9993   $24.00   $24.00   $24.00  
  Purchase #7 $81.97   12.293%   $92.0466   $92.05   $92.05   $92.00  
  7 purchase totals = $825.67       $909.0024   $909.01   $909.00   $908.90