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 $199.60   3.517%   $206.6199   $206.62   $206.60   $206.60  
  Purchase #2 $41.26   13.604%   $46.873   $46.87   $46.85   $46.90  
  Purchase #3 $158.60   4.212%   $165.2802   $165.28   $165.30   $165.30  
  Purchase #4 $108.95   7.220%   $116.8162   $116.82   $116.80   $116.80  
  Purchase #5 $84.79   10.695%   $93.8583   $93.86   $93.85   $93.90  
  Purchase #6 $128.92   8.482%   $139.855   $139.86   $139.85   $139.90  
  Purchase #7 $156.51   7.141%   $167.6864   $167.69   $167.70   $167.70  
  7 purchase totals = $878.63       $936.9890   $937.00   $936.95   $937.10