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 $107.86   6.838%   $115.2355   $115.24   $115.25   $115.20  
  Purchase #2 $172.74   6.623%   $184.1806   $184.18   $184.20   $184.20  
  Purchase #3 $163.99   6.146%   $174.0688   $174.07   $174.05   $174.10  
  Purchase #4 $197.44   12.316%   $221.7567   $221.76   $221.75   $221.80  
  Purchase #5 $139.78   5.756%   $147.8257   $147.83   $147.85   $147.80  
  Purchase #6 $117.91   5.709%   $124.6415   $124.64   $124.65   $124.60  
  Purchase #7 $41.38   11.806%   $46.2653   $46.27   $46.25   $46.30  
  7 purchase totals = $941.10       $1,013.9741   $1,013.99   $1,014.00   $1,014.00