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 $61.68   11.554%   $68.8065   $68.81   $68.80   $68.80  
  Purchase #2 $60.53   7.658%   $65.1654   $65.17   $65.15   $65.20  
  Purchase #3 $204.81   3.438%   $211.8514   $211.85   $211.85   $211.90  
  Purchase #4 $180.59   5.291%   $190.145   $190.15   $190.15   $190.10  
  Purchase #5 $249.89   11.396%   $278.3675   $278.37   $278.35   $278.40  
  Purchase #6 $142.34   3.271%   $146.9959   $147.00   $147.00   $147.00  
  Purchase #7 $88.72   10.782%   $98.2858   $98.29   $98.30   $98.30  
  7 purchase totals = $988.56       $1,059.6175   $1,059.64   $1,059.60   $1,059.70