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 $235.92   11.279%   $262.5294   $262.53   $262.55   $262.50  
  Purchase #2 $94.62   5.751%   $100.0616   $100.06   $100.05   $100.10  
  Purchase #3 $52.80   11.588%   $58.9185   $58.92   $58.90   $58.90  
  Purchase #4 $90.84   13.592%   $103.187   $103.19   $103.20   $103.20  
  Purchase #5 $120.91   11.829%   $135.2124   $135.21   $135.20   $135.20  
  Purchase #6 $127.94   3.799%   $132.8004   $132.80   $132.80   $132.80  
  Purchase #7 $233.94   9.411%   $255.9561   $255.96   $255.95   $256.00  
  7 purchase totals = $956.97       $1,048.6654   $1,048.67   $1,048.65   $1,048.70