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 $246.44   9.408%   $269.6251   $269.63   $269.65   $269.60  
  Purchase #2 $78.66   4.653%   $82.32   $82.32   $82.30   $82.30  
  Purchase #3 $20.52   7.822%   $22.1251   $22.13   $22.15   $22.10  
  Purchase #4 $6.26   7.465%   $6.7273   $6.73   $6.75   $6.70  
  Purchase #5 $169.54   11.654%   $189.2982   $189.30   $189.30   $189.30  
  Purchase #6 $185.57   8.272%   $200.9204   $200.92   $200.90   $200.90  
  Purchase #7 $125.33   4.532%   $131.01   $131.01   $131.00   $131.00  
  7 purchase totals = $832.32       $902.0261   $902.04   $902.05   $901.90