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 $108.72   4.538%   $113.6537   $113.65   $113.65   $113.70  
  Purchase #2 $195.48   3.139%   $201.6161   $201.62   $201.60   $201.60  
  Purchase #3 $227.60   11.797%   $254.45   $254.45   $254.45   $254.50  
  Purchase #4 $85.25   10.544%   $94.2388   $94.24   $94.25   $94.20  
  Purchase #5 $83.85   13.172%   $94.8947   $94.89   $94.90   $94.90  
  Purchase #6 $126.68   4.162%   $131.9524   $131.95   $131.95   $132.00  
  Purchase #7 $117.82   11.119%   $130.9204   $130.92   $130.90   $130.90  
  7 purchase totals = $945.40       $1,021.7261   $1,021.72   $1,021.70   $1,021.80