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 $150.88   6.741%   $161.0508   $161.05   $161.05   $161.10  
  Purchase #2 $170.82   13.294%   $193.5288   $193.53   $193.55   $193.50  
  Purchase #3 $214.65   5.706%   $226.8979   $226.90   $226.90   $226.90  
  Purchase #4 $218.76   10.656%   $242.0711   $242.07   $242.05   $242.10  
  Purchase #5 $32.36   3.637%   $33.5369   $33.54   $33.55   $33.50  
  Purchase #6 $237.87   13.663%   $270.3702   $270.37   $270.35   $270.40  
  Purchase #7 $126.80   3.412%   $131.1264   $131.13   $131.15   $131.10  
  7 purchase totals = $1,152.14       $1,258.5821   $1,258.59   $1,258.60   $1,258.60