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 $67.76   4.325%   $70.6906   $70.69   $70.70   $70.70  
  Purchase #2 $192.41   4.680%   $201.4148   $201.41   $201.40   $201.40  
  Purchase #3 $86.58   6.839%   $92.5012   $92.50   $92.50   $92.50  
  Purchase #4 $233.29   12.358%   $262.12   $262.12   $262.10   $262.10  
  Purchase #5 $191.91   11.842%   $214.636   $214.64   $214.65   $214.60  
  Purchase #6 $29.53   12.438%   $33.2029   $33.20   $33.20   $33.20  
  Purchase #7 $142.52   13.412%   $161.6348   $161.63   $161.65   $161.60  
  7 purchase totals = $944.00       $1,036.2003   $1,036.19   $1,036.20   $1,036.10