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 $116.56   8.421%   $126.3755   $126.38   $126.40   $126.40  
  Purchase #2 $212.28   12.140%   $238.0508   $238.05   $238.05   $238.10  
  Purchase #3 $14.89   10.827%   $16.5021   $16.50   $16.50   $16.50  
  Purchase #4 $150.54   13.657%   $171.0992   $171.10   $171.10   $171.10  
  Purchase #5 $10.26   13.145%   $11.6087   $11.61   $11.60   $11.60  
  Purchase #6 $122.47   8.289%   $132.6215   $132.62   $132.60   $132.60  
  Purchase #7 $248.56   13.794%   $282.8464   $282.85   $282.85   $282.80  
  7 purchase totals = $875.56       $979.1042   $979.11   $979.10   $979.10