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 $187.38   13.502%   $212.68   $212.68   $212.70   $212.70  
  Purchase #2 $82.25   4.518%   $85.9661   $85.97   $85.95   $86.00  
  Purchase #3 $64.63   13.227%   $73.1786   $73.18   $73.20   $73.20  
  Purchase #4 $228.72   11.495%   $255.0114   $255.01   $255.00   $255.00  
  Purchase #5 $32.31   7.622%   $34.7727   $34.77   $34.75   $34.80  
  Purchase #6 $237.26   6.219%   $252.0152   $252.02   $252.00   $252.00  
  Purchase #7 $146.65   3.202%   $151.3457   $151.35   $151.35   $151.30  
  7 purchase totals = $979.20       $1,064.9697   $1,064.98   $1,064.95   $1,065.00