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 $110.85   12.578%   $124.7927   $124.79   $124.80   $124.80  
  Purchase #2 $11.38   7.556%   $12.2399   $12.24   $12.25   $12.20  
  Purchase #3 $60.38   5.316%   $63.5898   $63.59   $63.60   $63.60  
  Purchase #4 $244.96   8.670%   $266.198   $266.20   $266.20   $266.20  
  Purchase #5 $235.50   8.310%   $255.0701   $255.07   $255.05   $255.10  
  Purchase #6 $111.85   7.474%   $120.2097   $120.21   $120.20   $120.20  
  Purchase #7 $207.42   9.465%   $227.0523   $227.05   $227.05   $227.10  
  7 purchase totals = $982.34       $1,069.1525   $1,069.15   $1,069.15   $1,069.20