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 $161.93   10.311%   $178.6266   $178.63   $178.65   $178.60  
  Purchase #2 $228.32   7.452%   $245.3344   $245.33   $245.35   $245.30  
  Purchase #3 $143.63   11.148%   $159.6419   $159.64   $159.65   $159.60  
  Purchase #4 $48.38   7.561%   $52.038   $52.04   $52.05   $52.00  
  Purchase #5 $211.82   8.438%   $229.6934   $229.69   $229.70   $229.70  
  Purchase #6 $30.70   8.279%   $33.2417   $33.24   $33.25   $33.20  
  Purchase #7 $149.59   11.187%   $166.3246   $166.32   $166.30   $166.30  
  7 purchase totals = $974.37       $1,064.9006   $1,064.89   $1,064.95   $1,064.70