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 $149.48   6.549%   $159.2694   $159.27   $159.25   $159.30  
  Purchase #2 $244.28   13.662%   $277.6535   $277.65   $277.65   $277.70  
  Purchase #3 $68.80   3.469%   $71.1867   $71.19   $71.20   $71.20  
  Purchase #4 $228.36   6.159%   $242.4247   $242.42   $242.40   $242.40  
  Purchase #5 $41.67   7.665%   $44.864   $44.86   $44.85   $44.90  
  Purchase #6 $110.84   12.183%   $124.3436   $124.34   $124.35   $124.30  
  Purchase #7 $80.60   5.253%   $84.8339   $84.83   $84.85   $84.80  
  7 purchase totals = $924.03       $1,004.5758   $1,004.56   $1,004.55   $1,004.60