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 $248.28   4.836%   $260.2868   $260.29   $260.30   $260.30  
  Purchase #2 $87.76   5.728%   $92.7869   $92.79   $92.80   $92.80  
  Purchase #3 $81.43   4.643%   $85.2108   $85.21   $85.20   $85.20  
  Purchase #4 $170.53   12.629%   $192.0662   $192.07   $192.05   $192.10  
  Purchase #5 $69.60   11.208%   $77.4008   $77.40   $77.40   $77.40  
  Purchase #6 $232.69   9.117%   $253.9043   $253.90   $253.90   $253.90  
  Purchase #7 $49.66   4.871%   $52.0789   $52.08   $52.10   $52.10  
  7 purchase totals = $939.95       $1,013.7347   $1,013.74   $1,013.75   $1,013.80