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 $221.88   13.701%   $252.2798   $252.28   $252.30   $252.30  
  Purchase #2 $138.64   3.400%   $143.3538   $143.35   $143.35   $143.40  
  Purchase #3 $235.84   8.733%   $256.4359   $256.44   $256.45   $256.40  
  Purchase #4 $182.97   6.193%   $194.3013   $194.30   $194.30   $194.30  
  Purchase #5 $57.28   5.741%   $60.5684   $60.57   $60.55   $60.60  
  Purchase #6 $193.32   11.595%   $215.7355   $215.74   $215.75   $215.70  
  Purchase #7 $49.64   5.560%   $52.4   $52.40   $52.40   $52.40  
  7 purchase totals = $1,079.57       $1,175.0747   $1,175.08   $1,175.10   $1,175.10