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 $157.99   10.762%   $174.9929   $174.99   $175.00   $175.00  
  Purchase #2 $54.58   3.817%   $56.6633   $56.66   $56.65   $56.70  
  Purchase #3 $162.38   7.119%   $173.9398   $173.94   $173.95   $173.90  
  Purchase #4 $230.46   4.270%   $240.3006   $240.30   $240.30   $240.30  
  Purchase #5 $141.93   4.821%   $148.7724   $148.77   $148.75   $148.80  
  Purchase #6 $237.73   13.532%   $269.8996   $269.90   $269.90   $269.90  
  Purchase #7 $215.49   6.706%   $229.9408   $229.94   $229.95   $229.90  
  7 purchase totals = $1,200.56       $1,294.5094   $1,294.50   $1,294.50   $1,294.50