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 $42.32   5.677%   $44.7225   $44.72   $44.70   $44.70  
  Purchase #2 $233.70   6.277%   $248.3693   $248.37   $248.35   $248.40  
  Purchase #3 $113.36   5.697%   $119.8181   $119.82   $119.80   $119.80  
  Purchase #4 $225.56   9.503%   $246.995   $247.00   $247.00   $247.00  
  Purchase #5 $235.68   7.149%   $252.5288   $252.53   $252.55   $252.50  
  Purchase #6 $32.43   11.536%   $36.1711   $36.17   $36.15   $36.20  
  Purchase #7 $111.84   3.400%   $115.6426   $115.64   $115.65   $115.60  
  7 purchase totals = $994.89       $1,064.2474   $1,064.25   $1,064.20   $1,064.20