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 $57.41   4.563%   $60.0296   $60.03   $60.05   $60.00  
  Purchase #2 $96.32   13.553%   $109.3742   $109.37   $109.35   $109.40  
  Purchase #3 $139.68   7.480%   $150.1281   $150.13   $150.15   $150.10  
  Purchase #4 $154.94   6.194%   $164.537   $164.54   $164.55   $164.50  
  Purchase #5 $204.85   3.765%   $212.5626   $212.56   $212.55   $212.60  
  Purchase #6 $10.48   10.548%   $11.5854   $11.59   $11.60   $11.60  
  Purchase #7 $112.26   12.636%   $126.4452   $126.45   $126.45   $126.40  
  7 purchase totals = $775.94       $834.6621   $834.67   $834.70   $834.60