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 $199.87   7.217%   $214.2946   $214.29   $214.30   $214.30  
  Purchase #2 $149.28   12.530%   $167.9848   $167.98   $168.00   $168.00  
  Purchase #3 $122.45   6.733%   $130.6946   $130.69   $130.70   $130.70  
  Purchase #4 $250.97   9.186%   $274.0241   $274.02   $274.00   $274.00  
  Purchase #5 $187.77   3.228%   $193.8312   $193.83   $193.85   $193.80  
  Purchase #6 $41.52   7.774%   $44.7478   $44.75   $44.75   $44.70  
  Purchase #7 $17.67   3.650%   $18.315   $18.32   $18.30   $18.30  
  7 purchase totals = $969.53       $1,043.8921   $1,043.88   $1,043.90   $1,043.80