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 $11.65   11.201%   $12.9549   $12.95   $12.95   $13.00  
  Purchase #2 $208.83   8.293%   $226.1483   $226.15   $226.15   $226.10  
  Purchase #3 $152.74   8.616%   $165.9001   $165.90   $165.90   $165.90  
  Purchase #4 $119.80   3.830%   $124.3883   $124.39   $124.40   $124.40  
  Purchase #5 $112.42   7.771%   $121.1562   $121.16   $121.15   $121.20  
  Purchase #6 $116.90   7.723%   $125.9282   $125.93   $125.95   $125.90  
  Purchase #7 $83.62   4.374%   $87.2775   $87.28   $87.30   $87.30  
  7 purchase totals = $805.96       $863.7535   $863.76   $863.80   $863.80