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 $219.45   12.375%   $246.6069   $246.61   $246.60   $246.60  
  Purchase #2 $83.78   3.418%   $86.6436   $86.64   $86.65   $86.60  
  Purchase #3 $41.89   6.251%   $44.5085   $44.51   $44.50   $44.50  
  Purchase #4 $125.62   9.595%   $137.6732   $137.67   $137.65   $137.70  
  Purchase #5 $120.62   11.276%   $134.2211   $134.22   $134.20   $134.20  
  Purchase #6 $171.57   6.537%   $182.7855   $182.79   $182.80   $182.80  
  Purchase #7 $184.66   10.739%   $204.4906   $204.49   $204.50   $204.50  
  7 purchase totals = $947.59       $1,036.9294   $1,036.93   $1,036.90   $1,036.90