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 $108.82   13.596%   $123.6152   $123.62   $123.60   $123.60  
  Purchase #2 $226.32   11.800%   $253.0258   $253.03   $253.05   $253.00  
  Purchase #3 $198.35   12.626%   $223.3937   $223.39   $223.40   $223.40  
  Purchase #4 $197.73   4.688%   $206.9996   $207.00   $207.00   $207.00  
  Purchase #5 $46.48   4.493%   $48.5683   $48.57   $48.55   $48.60  
  Purchase #6 $228.25   12.373%   $256.4914   $256.49   $256.50   $256.50  
  Purchase #7 $20.87   11.808%   $23.3343   $23.33   $23.35   $23.30  
  7 purchase totals = $1,026.82       $1,135.4283   $1,135.43   $1,135.45   $1,135.40