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 $192.97   8.368%   $209.1177   $209.12   $209.10   $209.10  
  Purchase #2 $117.95   4.159%   $122.8555   $122.86   $122.85   $122.90  
  Purchase #3 $176.80   10.295%   $195.0016   $195.00   $195.00   $195.00  
  Purchase #4 $46.75   11.331%   $52.0472   $52.05   $52.05   $52.00  
  Purchase #5 $163.67   10.502%   $180.8586   $180.86   $180.85   $180.90  
  Purchase #6 $131.59   3.371%   $136.0259   $136.03   $136.05   $136.00  
  Purchase #7 $60.46   13.749%   $68.7726   $68.77   $68.75   $68.80  
  7 purchase totals = $890.19       $964.6791   $964.69   $964.65   $964.70