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 $226.37   8.118%   $244.7467   $244.75   $244.75   $244.70  
  Purchase #2 $205.53   3.484%   $212.6907   $212.69   $212.70   $212.70  
  Purchase #3 $240.94   11.554%   $268.7782   $268.78   $268.80   $268.80  
  Purchase #4 $197.90   3.648%   $205.1194   $205.12   $205.10   $205.10  
  Purchase #5 $28.33   7.395%   $30.425   $30.43   $30.45   $30.40  
  Purchase #6 $200.80   11.649%   $224.1912   $224.19   $224.20   $224.20  
  Purchase #7 $190.27   3.470%   $196.8724   $196.87   $196.85   $196.90  
  7 purchase totals = $1,290.14       $1,382.8236   $1,382.83   $1,382.85   $1,382.80