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 $56.40   5.431%   $59.4631   $59.46   $59.45   $59.50  
  Purchase #2 $181.61   13.560%   $206.2363   $206.24   $206.25   $206.20  
  Purchase #3 $64.60   10.833%   $71.5981   $71.60   $71.60   $71.60  
  Purchase #4 $8.33   6.232%   $8.8491   $8.85   $8.85   $8.80  
  Purchase #5 $118.83   4.148%   $123.7591   $123.76   $123.75   $123.80  
  Purchase #6 $37.78   10.372%   $41.6985   $41.70   $41.70   $41.70  
  Purchase #7 $197.71   8.613%   $214.7388   $214.74   $214.75   $214.70  
  7 purchase totals = $665.26       $726.3430   $726.35   $726.35   $726.30