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 $226.55   8.297%   $245.3469   $245.35   $245.35   $245.30  
  Purchase #2 $164.34   5.607%   $173.5545   $173.55   $173.55   $173.60  
  Purchase #3 $250.26   11.356%   $278.6795   $278.68   $278.70   $278.70  
  Purchase #4 $237.60   5.140%   $249.8126   $249.81   $249.80   $249.80  
  Purchase #5 $129.76   13.304%   $147.0233   $147.02   $147.00   $147.00  
  Purchase #6 $14.59   8.401%   $15.8157   $15.82   $15.80   $15.80  
  Purchase #7 $244.34   7.250%   $262.0547   $262.05   $262.05   $262.10  
  7 purchase totals = $1,267.44       $1,372.2872   $1,372.28   $1,372.25   $1,372.30