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 $63.82   11.154%   $70.9385   $70.94   $70.95   $70.90  
  Purchase #2 $80.97   10.866%   $89.7682   $89.77   $89.75   $89.80  
  Purchase #3 $238.52   5.727%   $252.18   $252.18   $252.20   $252.20  
  Purchase #4 $63.82   4.541%   $66.7181   $66.72   $66.70   $66.70  
  Purchase #5 $20.37   6.205%   $21.634   $21.63   $21.65   $21.60  
  Purchase #6 $242.99   4.704%   $254.4202   $254.42   $254.40   $254.40  
  Purchase #7 $43.25   13.233%   $48.9733   $48.97   $48.95   $49.00  
  7 purchase totals = $753.74       $804.6323   $804.63   $804.60   $804.60