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 $92.78   6.360%   $98.6808   $98.68   $98.70   $98.70  
  Purchase #2 $217.69   8.280%   $235.7147   $235.71   $235.70   $235.70  
  Purchase #3 $89.70   12.614%   $101.0148   $101.01   $101.00   $101.00  
  Purchase #4 $50.53   12.299%   $56.7447   $56.74   $56.75   $56.70  
  Purchase #5 $65.76   12.271%   $73.8294   $73.83   $73.85   $73.80  
  Purchase #6 $56.45   13.478%   $64.0583   $64.06   $64.05   $64.10  
  Purchase #7 $88.86   13.757%   $101.0845   $101.08   $101.10   $101.10  
  7 purchase totals = $661.77       $731.1272   $731.11   $731.15   $731.10