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 $48.83   12.874%   $55.1164   $55.12   $55.10   $55.10  
  Purchase #2 $244.34   10.228%   $269.3311   $269.33   $269.35   $269.30  
  Purchase #3 $234.99   9.207%   $256.6255   $256.63   $256.65   $256.60  
  Purchase #4 $242.69   11.518%   $270.643   $270.64   $270.65   $270.60  
  Purchase #5 $215.79   6.397%   $229.5941   $229.59   $229.60   $229.60  
  Purchase #6 $37.62   10.683%   $41.6389   $41.64   $41.65   $41.60  
  Purchase #7 $193.83   6.142%   $205.735   $205.74   $205.75   $205.70  
  7 purchase totals = $1,218.09       $1,328.6840   $1,328.69   $1,328.75   $1,328.50