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 $73.27   11.393%   $81.6177   $81.62   $81.60   $81.60  
  Purchase #2 $236.76   8.267%   $256.3329   $256.33   $256.35   $256.30  
  Purchase #3 $176.30   9.830%   $193.6303   $193.63   $193.65   $193.60  
  Purchase #4 $72.86   9.239%   $79.5915   $79.59   $79.60   $79.60  
  Purchase #5 $116.74   9.236%   $127.5221   $127.52   $127.50   $127.50  
  Purchase #6 $216.42   13.195%   $244.9766   $244.98   $245.00   $245.00  
  Purchase #7 $75.37   11.410%   $83.9697   $83.97   $83.95   $84.00  
  7 purchase totals = $967.72       $1,067.6408   $1,067.64   $1,067.65   $1,067.60