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 $117.77   10.394%   $130.011   $130.01   $130.00   $130.00  
  Purchase #2 $190.83   11.276%   $212.348   $212.35   $212.35   $212.30  
  Purchase #3 $94.49   5.716%   $99.891   $99.89   $99.90   $99.90  
  Purchase #4 $239.60   4.844%   $251.2062   $251.21   $251.20   $251.20  
  Purchase #5 $173.66   8.202%   $187.9036   $187.90   $187.90   $187.90  
  Purchase #6 $97.72   6.650%   $104.2184   $104.22   $104.20   $104.20  
  Purchase #7 $30.25   8.524%   $32.8285   $32.83   $32.85   $32.80  
  7 purchase totals = $944.32       $1,018.4067   $1,018.41   $1,018.40   $1,018.30