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 $240.99   9.560%   $264.0286   $264.03   $264.05   $264.00  
  Purchase #2 $213.71   7.226%   $229.1527   $229.15   $229.15   $229.20  
  Purchase #3 $164.77   8.818%   $179.2994   $179.30   $179.30   $179.30  
  Purchase #4 $97.83   13.231%   $110.7739   $110.77   $110.75   $110.80  
  Purchase #5 $214.45   4.595%   $224.304   $224.30   $224.30   $224.30  
  Purchase #6 $70.58   3.310%   $72.9162   $72.92   $72.90   $72.90  
  Purchase #7 $170.35   5.839%   $180.2967   $180.30   $180.30   $180.30  
  7 purchase totals = $1,172.68       $1,260.7715   $1,260.77   $1,260.75   $1,260.80