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 $93.40   5.532%   $98.5669   $98.57   $98.55   $98.60  
  Purchase #2 $140.46   13.458%   $159.3631   $159.36   $159.35   $159.40  
  Purchase #3 $95.78   4.528%   $100.1169   $100.12   $100.10   $100.10  
  Purchase #4 $129.74   12.464%   $145.9108   $145.91   $145.90   $145.90  
  Purchase #5 $206.56   13.711%   $234.8814   $234.88   $234.90   $234.90  
  Purchase #6 $163.43   7.770%   $176.1285   $176.13   $176.15   $176.10  
  Purchase #7 $86.85   12.597%   $97.7905   $97.79   $97.80   $97.80  
  7 purchase totals = $916.22       $1,012.7581   $1,012.76   $1,012.75   $1,012.80