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 $72.39   9.437%   $79.2214   $79.22   $79.20   $79.20  
  Purchase #2 $175.82   6.154%   $186.64   $186.64   $186.65   $186.60  
  Purchase #3 $53.97   13.381%   $61.1917   $61.19   $61.20   $61.20  
  Purchase #4 $170.42   13.857%   $194.0351   $194.04   $194.05   $194.00  
  Purchase #5 $83.38   4.589%   $87.2063   $87.21   $87.20   $87.20  
  Purchase #6 $223.96   11.465%   $249.637   $249.64   $249.65   $249.60  
  Purchase #7 $169.79   3.649%   $175.9856   $175.99   $176.00   $176.00  
  7 purchase totals = $949.73       $1,033.9171   $1,033.93   $1,033.95   $1,033.80