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 $204.27   8.820%   $222.2866   $222.29   $222.30   $222.30  
  Purchase #2 $34.39   5.206%   $36.1803   $36.18   $36.20   $36.20  
  Purchase #3 $110.87   6.293%   $117.847   $117.85   $117.85   $117.80  
  Purchase #4 $209.29   7.258%   $224.4803   $224.48   $224.50   $224.50  
  Purchase #5 $48.48   10.643%   $53.6397   $53.64   $53.65   $53.60  
  Purchase #6 $69.83   13.382%   $79.1747   $79.17   $79.15   $79.20  
  Purchase #7 $150.26   10.228%   $165.6286   $165.63   $165.65   $165.60  
  7 purchase totals = $827.39       $899.2372   $899.24   $899.30   $899.20