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 $34.72   8.329%   $37.6118   $37.61   $37.60   $37.60  
  Purchase #2 $44.81   13.246%   $50.7455   $50.75   $50.75   $50.70  
  Purchase #3 $149.64   10.280%   $165.023   $165.02   $165.00   $165.00  
  Purchase #4 $172.37   9.262%   $188.3349   $188.33   $188.35   $188.30  
  Purchase #5 $216.93   6.639%   $231.332   $231.33   $231.35   $231.30  
  Purchase #6 $96.66   6.627%   $103.0657   $103.07   $103.05   $103.10  
  Purchase #7 $66.26   11.452%   $73.8481   $73.85   $73.85   $73.80  
  7 purchase totals = $781.39       $849.9610   $849.96   $849.95   $849.80