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 $210.91   7.382%   $226.4794   $226.48   $226.50   $226.50  
  Purchase #2 $230.54   8.839%   $250.9174   $250.92   $250.90   $250.90  
  Purchase #3 $130.81   11.374%   $145.6883   $145.69   $145.70   $145.70  
  Purchase #4 $50.79   3.410%   $52.5219   $52.52   $52.50   $52.50  
  Purchase #5 $120.94   3.718%   $125.4365   $125.44   $125.45   $125.40  
  Purchase #6 $241.64   5.795%   $255.643   $255.64   $255.65   $255.60  
  Purchase #7 $187.60   10.387%   $207.086   $207.09   $207.10   $207.10  
  7 purchase totals = $1,173.23       $1,263.7725   $1,263.78   $1,263.80   $1,263.70