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 $76.96   8.567%   $83.5532   $83.55   $83.55   $83.60  
  Purchase #2 $200.38   12.796%   $226.0206   $226.02   $226.00   $226.00  
  Purchase #3 $120.77   3.214%   $124.6515   $124.65   $124.65   $124.70  
  Purchase #4 $115.51   8.817%   $125.6945   $125.69   $125.70   $125.70  
  Purchase #5 $39.64   12.554%   $44.6164   $44.62   $44.60   $44.60  
  Purchase #6 $239.35   6.281%   $254.3836   $254.38   $254.40   $254.40  
  Purchase #7 $6.44   9.781%   $7.0699   $7.07   $7.05   $7.10  
  7 purchase totals = $799.05       $865.9897   $865.98   $865.95   $866.10