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 $82.73   12.371%   $92.9645   $92.96   $92.95   $93.00  
  Purchase #2 $107.82   4.414%   $112.5792   $112.58   $112.60   $112.60  
  Purchase #3 $126.74   4.462%   $132.3951   $132.40   $132.40   $132.40  
  Purchase #4 $155.68   6.465%   $165.7447   $165.74   $165.75   $165.70  
  Purchase #5 $8.92   9.302%   $9.7497   $9.75   $9.75   $9.70  
  Purchase #6 $230.80   9.722%   $253.2384   $253.24   $253.25   $253.20  
  Purchase #7 $36.94   6.304%   $39.2687   $39.27   $39.25   $39.30  
  7 purchase totals = $749.63       $805.9403   $805.94   $805.95   $805.90