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 $229.70   5.844%   $243.1237   $243.12   $243.10   $243.10  
  Purchase #2 $198.91   9.771%   $218.3455   $218.35   $218.35   $218.30  
  Purchase #3 $104.56   12.438%   $117.5652   $117.57   $117.55   $117.60  
  Purchase #4 $116.72   10.384%   $128.8402   $128.84   $128.85   $128.80  
  Purchase #5 $159.63   3.863%   $165.7965   $165.80   $165.80   $165.80  
  Purchase #6 $46.59   9.682%   $51.1008   $51.10   $51.10   $51.10  
  Purchase #7 $96.91   3.243%   $100.0528   $100.05   $100.05   $100.10  
  7 purchase totals = $953.02       $1,024.8247   $1,024.83   $1,024.80   $1,024.80