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 $192.31   7.271%   $206.2929   $206.29   $206.30   $206.30  
  Purchase #2 $19.29   6.707%   $20.5838   $20.58   $20.60   $20.60  
  Purchase #3 $160.51   6.586%   $171.0812   $171.08   $171.10   $171.10  
  Purchase #4 $237.37   5.492%   $250.4064   $250.41   $250.40   $250.40  
  Purchase #5 $167.27   11.723%   $186.8791   $186.88   $186.90   $186.90  
  Purchase #6 $230.26   11.750%   $257.3156   $257.32   $257.30   $257.30  
  Purchase #7 $157.55   11.585%   $175.8022   $175.80   $175.80   $175.80  
  7 purchase totals = $1,164.56       $1,268.3612   $1,268.36   $1,268.40   $1,268.40