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 $245.61   5.776%   $259.7964   $259.80   $259.80   $259.80  
  Purchase #2 $192.61   8.319%   $208.6332   $208.63   $208.65   $208.60  
  Purchase #3 $83.89   4.787%   $87.9058   $87.91   $87.90   $87.90  
  Purchase #4 $112.45   11.259%   $125.1107   $125.11   $125.10   $125.10  
  Purchase #5 $53.32   7.119%   $57.1159   $57.12   $57.10   $57.10  
  Purchase #6 $226.92   3.614%   $235.1209   $235.12   $235.10   $235.10  
  Purchase #7 $220.99   5.727%   $233.6461   $233.65   $233.65   $233.60  
  7 purchase totals = $1,135.79       $1,207.3290   $1,207.34   $1,207.30   $1,207.20