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 $7.32   7.480%   $7.8675   $7.87   $7.85   $7.90  
  Purchase #2 $190.35   3.591%   $197.1855   $197.19   $197.20   $197.20  
  Purchase #3 $156.57   3.789%   $162.5024   $162.50   $162.50   $162.50  
  Purchase #4 $124.66   12.831%   $140.6551   $140.66   $140.65   $140.70  
  Purchase #5 $112.46   9.470%   $123.11   $123.11   $123.10   $123.10  
  Purchase #6 $20.98   13.338%   $23.7783   $23.78   $23.80   $23.80  
  Purchase #7 $5.43   11.361%   $6.0469   $6.05   $6.05   $6.00  
  7 purchase totals = $617.77       $661.1457   $661.16   $661.15   $661.20