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 $52.33   7.519%   $56.2647   $56.26   $56.25   $56.30  
  Purchase #2 $169.39   10.839%   $187.7502   $187.75   $187.75   $187.80  
  Purchase #3 $139.42   12.696%   $157.1208   $157.12   $157.10   $157.10  
  Purchase #4 $213.76   13.633%   $242.9019   $242.90   $242.90   $242.90  
  Purchase #5 $125.46   3.731%   $130.1409   $130.14   $130.15   $130.10  
  Purchase #6 $24.65   10.705%   $27.2888   $27.29   $27.30   $27.30  
  Purchase #7 $189.38   13.396%   $214.7493   $214.75   $214.75   $214.70  
  7 purchase totals = $914.39       $1,016.2166   $1,016.21   $1,016.20   $1,016.20