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 $211.27   5.841%   $223.6103   $223.61   $223.60   $223.60  
  Purchase #2 $7.27   12.105%   $8.15   $8.15   $8.15   $8.20  
  Purchase #3 $64.75   7.620%   $69.684   $69.68   $69.70   $69.70  
  Purchase #4 $145.43   4.850%   $152.4834   $152.48   $152.50   $152.50  
  Purchase #5 $168.78   5.171%   $177.5076   $177.51   $177.50   $177.50  
  Purchase #6 $153.62   7.212%   $164.6991   $164.70   $164.70   $164.70  
  Purchase #7 $179.77   3.237%   $185.5892   $185.59   $185.60   $185.60  
  7 purchase totals = $930.89       $981.7236   $981.72   $981.75   $981.80