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 $57.49   6.821%   $61.4114   $61.41   $61.40   $61.40  
  Purchase #2 $188.40   4.859%   $197.5544   $197.55   $197.55   $197.60  
  Purchase #3 $203.57   7.452%   $218.74   $218.74   $218.75   $218.70  
  Purchase #4 $128.65   11.166%   $143.0151   $143.02   $143.00   $143.00  
  Purchase #5 $146.67   5.868%   $155.2766   $155.28   $155.30   $155.30  
  Purchase #6 $230.65   8.149%   $249.4457   $249.45   $249.45   $249.40  
  Purchase #7 $209.94   9.655%   $230.2097   $230.21   $230.20   $230.20  
  7 purchase totals = $1,165.37       $1,255.6529   $1,255.66   $1,255.65   $1,255.60