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 $56.59   4.802%   $59.3075   $59.31   $59.30   $59.30  
  Purchase #2 $177.44   12.652%   $199.8897   $199.89   $199.90   $199.90  
  Purchase #3 $174.31   11.379%   $194.1447   $194.14   $194.15   $194.10  
  Purchase #4 $63.31   8.318%   $68.5761   $68.58   $68.60   $68.60  
  Purchase #5 $191.31   11.288%   $212.9051   $212.91   $212.90   $212.90  
  Purchase #6 $180.98   9.853%   $198.812   $198.81   $198.80   $198.80  
  Purchase #7 $232.44   3.359%   $240.2477   $240.25   $240.25   $240.20  
  7 purchase totals = $1,076.38       $1,173.8828   $1,173.89   $1,173.90   $1,173.80