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 $44.40   6.489%   $47.2811   $47.28   $47.30   $47.30  
  Purchase #2 $244.48   6.632%   $260.6939   $260.69   $260.70   $260.70  
  Purchase #3 $124.61   7.107%   $133.466   $133.47   $133.45   $133.50  
  Purchase #4 $179.93   3.444%   $186.1268   $186.13   $186.15   $186.10  
  Purchase #5 $225.25   7.174%   $241.4094   $241.41   $241.40   $241.40  
  Purchase #6 $145.39   5.413%   $153.26   $153.26   $153.25   $153.30  
  Purchase #7 $228.36   11.365%   $254.3131   $254.31   $254.30   $254.30  
  7 purchase totals = $1,192.42       $1,276.5503   $1,276.55   $1,276.55   $1,276.60