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 $56.46   4.857%   $59.2023   $59.20   $59.20   $59.20  
  Purchase #2 $29.49   10.364%   $32.5463   $32.55   $32.55   $32.50  
  Purchase #3 $125.66   6.138%   $133.373   $133.37   $133.35   $133.40  
  Purchase #4 $36.99   6.569%   $39.4199   $39.42   $39.40   $39.40  
  Purchase #5 $163.31   4.504%   $170.6655   $170.67   $170.65   $170.70  
  Purchase #6 $239.34   11.694%   $267.3284   $267.33   $267.35   $267.30  
  Purchase #7 $171.59   5.669%   $181.3174   $181.32   $181.30   $181.30  
  7 purchase totals = $822.84       $883.8528   $883.86   $883.80   $883.80