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 $70.53   7.242%   $75.6378   $75.64   $75.65   $75.60  
  Purchase #2 $85.63   12.481%   $96.3175   $96.32   $96.30   $96.30  
  Purchase #3 $34.83   6.423%   $37.0671   $37.07   $37.05   $37.10  
  Purchase #4 $14.44   6.217%   $15.3377   $15.34   $15.35   $15.30  
  Purchase #5 $235.52   7.503%   $253.1911   $253.19   $253.20   $253.20  
  Purchase #6 $226.98   11.171%   $252.3359   $252.34   $252.35   $252.30  
  Purchase #7 $49.45   12.493%   $55.6278   $55.63   $55.65   $55.60  
  7 purchase totals = $717.38       $785.5149   $785.53   $785.55   $785.40