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 $206.45   3.663%   $214.0123   $214.01   $214.00   $214.00  
  Purchase #2 $75.45   11.151%   $83.8634   $83.86   $83.85   $83.90  
  Purchase #3 $221.99   3.403%   $229.5443   $229.54   $229.55   $229.50  
  Purchase #4 $139.96   10.387%   $154.4976   $154.50   $154.50   $154.50  
  Purchase #5 $169.61   4.322%   $176.9405   $176.94   $176.95   $176.90  
  Purchase #6 $181.98   6.529%   $193.8615   $193.86   $193.85   $193.90  
  Purchase #7 $214.57   13.217%   $242.9297   $242.93   $242.95   $242.90  
  7 purchase totals = $1,210.01       $1,295.6493   $1,295.64   $1,295.65   $1,295.60