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 $141.41   8.281%   $153.1202   $153.12   $153.10   $153.10  
  Purchase #2 $19.57   3.576%   $20.2698   $20.27   $20.25   $20.30  
  Purchase #3 $193.32   5.303%   $203.5718   $203.57   $203.55   $203.60  
  Purchase #4 $236.35   8.544%   $256.5437   $256.54   $256.55   $256.50  
  Purchase #5 $73.26   11.232%   $81.4886   $81.49   $81.50   $81.50  
  Purchase #6 $94.97   8.222%   $102.7784   $102.78   $102.80   $102.80  
  Purchase #7 $192.91   11.815%   $215.7023   $215.70   $215.70   $215.70  
  7 purchase totals = $951.79       $1,033.4748   $1,033.47   $1,033.45   $1,033.50