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 $62.66   13.793%   $71.3027   $71.30   $71.30   $71.30  
  Purchase #2 $212.45   13.313%   $240.7335   $240.73   $240.75   $240.70  
  Purchase #3 $87.47   9.795%   $96.0377   $96.04   $96.05   $96.00  
  Purchase #4 $173.32   5.607%   $183.0381   $183.04   $183.05   $183.00  
  Purchase #5 $174.63   7.791%   $188.2354   $188.24   $188.25   $188.20  
  Purchase #6 $145.76   5.505%   $153.7841   $153.78   $153.80   $153.80  
  Purchase #7 $82.70   4.643%   $86.5398   $86.54   $86.55   $86.50  
  7 purchase totals = $938.99       $1,019.6713   $1,019.67   $1,019.75   $1,019.50