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 $49.50   13.620%   $56.2419   $56.24   $56.25   $56.20  
  Purchase #2 $96.65   13.200%   $109.4078   $109.41   $109.40   $109.40  
  Purchase #3 $245.84   4.729%   $257.4658   $257.47   $257.45   $257.50  
  Purchase #4 $211.95   10.673%   $234.5714   $234.57   $234.55   $234.60  
  Purchase #5 $130.75   8.826%   $142.29   $142.29   $142.30   $142.30  
  Purchase #6 $146.99   3.747%   $152.4977   $152.50   $152.50   $152.50  
  Purchase #7 $180.56   7.718%   $194.4956   $194.50   $194.50   $194.50  
  7 purchase totals = $1,062.24       $1,146.9702   $1,146.98   $1,146.95   $1,147.00