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 $235.85   4.313%   $246.0222   $246.02   $246.00   $246.00  
  Purchase #2 $228.64   12.442%   $257.0874   $257.09   $257.10   $257.10  
  Purchase #3 $245.46   11.798%   $274.4194   $274.42   $274.40   $274.40  
  Purchase #4 $153.67   13.311%   $174.125   $174.13   $174.15   $174.10  
  Purchase #5 $23.59   11.385%   $26.2757   $26.28   $26.30   $26.30  
  Purchase #6 $37.71   10.685%   $41.7393   $41.74   $41.75   $41.70  
  Purchase #7 $226.41   13.394%   $256.7354   $256.74   $256.75   $256.70  
  7 purchase totals = $1,151.33       $1,276.4044   $1,276.42   $1,276.45   $1,276.30