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 $65.62   11.791%   $73.3573   $73.36   $73.35   $73.40  
  Purchase #2 $26.51   7.473%   $28.4911   $28.49   $28.50   $28.50  
  Purchase #3 $184.26   3.135%   $190.0366   $190.04   $190.05   $190.00  
  Purchase #4 $97.44   9.163%   $106.3684   $106.37   $106.35   $106.40  
  Purchase #5 $177.61   4.233%   $185.1282   $185.13   $185.15   $185.10  
  Purchase #6 $92.79   11.199%   $103.1816   $103.18   $103.20   $103.20  
  Purchase #7 $12.62   12.315%   $14.1742   $14.17   $14.15   $14.20  
  7 purchase totals = $656.85       $700.7374   $700.74   $700.75   $700.80