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 $69.25   11.523%   $77.2297   $77.23   $77.25   $77.20  
  Purchase #2 $27.53   5.743%   $29.111   $29.11   $29.10   $29.10  
  Purchase #3 $25.86   10.267%   $28.515   $28.52   $28.50   $28.50  
  Purchase #4 $244.31   8.648%   $265.4379   $265.44   $265.45   $265.40  
  Purchase #5 $70.88   5.622%   $74.8649   $74.86   $74.85   $74.90  
  Purchase #6 $22.96   8.721%   $24.9623   $24.96   $24.95   $25.00  
  Purchase #7 $164.34   4.796%   $172.2217   $172.22   $172.20   $172.20  
  7 purchase totals = $625.13       $672.3425   $672.34   $672.30   $672.30