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 $66.52   6.504%   $70.8465   $70.85   $70.85   $70.80  
  Purchase #2 $165.83   6.553%   $176.6968   $176.70   $176.70   $176.70  
  Purchase #3 $105.61   7.846%   $113.8962   $113.90   $113.90   $113.90  
  Purchase #4 $212.87   8.484%   $230.9299   $230.93   $230.95   $230.90  
  Purchase #5 $168.47   6.285%   $179.0583   $179.06   $179.05   $179.10  
  Purchase #6 $246.77   3.379%   $255.1084   $255.11   $255.10   $255.10  
  Purchase #7 $176.56   8.866%   $192.2138   $192.21   $192.20   $192.20  
  7 purchase totals = $1,142.63       $1,218.7499   $1,218.76   $1,218.75   $1,218.70