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 $234.82   5.314%   $247.2983   $247.30   $247.30   $247.30  
  Purchase #2 $226.91   9.214%   $247.8175   $247.82   $247.80   $247.80  
  Purchase #3 $52.47   5.177%   $55.1864   $55.19   $55.20   $55.20  
  Purchase #4 $137.66   5.685%   $145.486   $145.49   $145.50   $145.50  
  Purchase #5 $200.98   13.244%   $227.5978   $227.60   $227.60   $227.60  
  Purchase #6 $130.98   5.562%   $138.2651   $138.27   $138.25   $138.30  
  Purchase #7 $209.82   4.188%   $218.6073   $218.61   $218.60   $218.60  
  7 purchase totals = $1,193.64       $1,280.2584   $1,280.28   $1,280.25   $1,280.30