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 $93.68   8.658%   $101.7908   $101.79   $101.80   $101.80  
  Purchase #2 $206.77   8.811%   $224.9885   $224.99   $225.00   $225.00  
  Purchase #3 $89.42   12.117%   $100.255   $100.26   $100.25   $100.30  
  Purchase #4 $138.38   3.463%   $143.1721   $143.17   $143.15   $143.20  
  Purchase #5 $170.80   4.178%   $177.936   $177.94   $177.95   $177.90  
  Purchase #6 $151.51   8.696%   $164.6853   $164.69   $164.70   $164.70  
  Purchase #7 $142.75   4.414%   $149.051   $149.05   $149.05   $149.10  
  7 purchase totals = $993.31       $1,061.8787   $1,061.89   $1,061.90   $1,062.00