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 $154.98   13.324%   $175.6295   $175.63   $175.65   $175.60  
  Purchase #2 $212.77   13.366%   $241.2088   $241.21   $241.20   $241.20  
  Purchase #3 $16.67   11.786%   $18.6347   $18.63   $18.65   $18.60  
  Purchase #4 $231.52   4.426%   $241.7671   $241.77   $241.75   $241.80  
  Purchase #5 $34.41   5.719%   $36.3779   $36.38   $36.40   $36.40  
  Purchase #6 $178.62   8.343%   $193.5223   $193.52   $193.50   $193.50  
  Purchase #7 $194.77   5.785%   $206.0374   $206.04   $206.05   $206.00  
  7 purchase totals = $1,023.74       $1,113.1777   $1,113.18   $1,113.20   $1,113.10