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 $207.28   9.256%   $226.4658   $226.47   $226.45   $226.50  
  Purchase #2 $22.37   8.342%   $24.2361   $24.24   $24.25   $24.20  
  Purchase #3 $36.28   9.818%   $39.842   $39.84   $39.85   $39.80  
  Purchase #4 $66.41   5.309%   $69.9357   $69.94   $69.95   $69.90  
  Purchase #5 $169.62   13.217%   $192.0387   $192.04   $192.05   $192.00  
  Purchase #6 $214.99   8.667%   $233.6232   $233.62   $233.60   $233.60  
  Purchase #7 $207.31   4.173%   $215.961   $215.96   $215.95   $216.00  
  7 purchase totals = $924.26       $1,002.1025   $1,002.11   $1,002.10   $1,002.00