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 $217.98   12.817%   $245.9185   $245.92   $245.90   $245.90  
  Purchase #2 $114.25   8.568%   $124.0389   $124.04   $124.05   $124.00  
  Purchase #3 $18.46   11.190%   $20.5257   $20.53   $20.55   $20.50  
  Purchase #4 $37.42   3.823%   $38.8506   $38.85   $38.85   $38.90  
  Purchase #5 $75.90   6.668%   $80.961   $80.96   $80.95   $81.00  
  Purchase #6 $250.38   10.749%   $277.2933   $277.29   $277.30   $277.30  
  Purchase #7 $203.57   6.430%   $216.6596   $216.66   $216.65   $216.70  
  7 purchase totals = $917.96       $1,004.2476   $1,004.25   $1,004.25   $1,004.30