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 $243.68   13.445%   $276.4428   $276.44   $276.45   $276.40  
  Purchase #2 $55.76   11.266%   $62.0419   $62.04   $62.05   $62.00  
  Purchase #3 $45.66   13.806%   $51.9638   $51.96   $51.95   $52.00  
  Purchase #4 $83.36   3.544%   $86.3143   $86.31   $86.30   $86.30  
  Purchase #5 $231.30   6.590%   $246.5427   $246.54   $246.55   $246.50  
  Purchase #6 $137.81   13.775%   $156.7933   $156.79   $156.80   $156.80  
  Purchase #7 $137.40   12.239%   $154.2164   $154.22   $154.20   $154.20  
  7 purchase totals = $934.97       $1,034.3152   $1,034.30   $1,034.30   $1,034.20