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 $241.42   10.747%   $267.3654   $267.37   $267.35   $267.40  
  Purchase #2 $176.70   9.276%   $193.0907   $193.09   $193.10   $193.10  
  Purchase #3 $24.52   5.857%   $25.9561   $25.96   $25.95   $26.00  
  Purchase #4 $160.52   5.121%   $168.7402   $168.74   $168.75   $168.70  
  Purchase #5 $129.89   9.211%   $141.8542   $141.85   $141.85   $141.90  
  Purchase #6 $168.27   10.314%   $185.6254   $185.63   $185.65   $185.60  
  Purchase #7 $50.86   8.133%   $54.9964   $55.00   $55.00   $55.00  
  7 purchase totals = $952.18       $1,037.6284   $1,037.64   $1,037.65   $1,037.70