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 $144.34   13.361%   $163.6253   $163.63   $163.65   $163.60  
  Purchase #2 $108.65   4.202%   $113.2155   $113.22   $113.20   $113.20  
  Purchase #3 $160.90   13.123%   $182.0149   $182.01   $182.00   $182.00  
  Purchase #4 $149.68   11.555%   $166.9755   $166.98   $167.00   $167.00  
  Purchase #5 $200.44   13.105%   $226.7077   $226.71   $226.70   $226.70  
  Purchase #6 $78.34   13.585%   $88.9825   $88.98   $89.00   $89.00  
  Purchase #7 $156.91   6.688%   $167.4041   $167.40   $167.40   $167.40  
  7 purchase totals = $999.26       $1,108.9255   $1,108.93   $1,108.95   $1,108.90