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 $87.87   10.290%   $96.9118   $96.91   $96.90   $96.90  
  Purchase #2 $69.26   6.293%   $73.6185   $73.62   $73.60   $73.60  
  Purchase #3 $188.51   7.481%   $202.6124   $202.61   $202.60   $202.60  
  Purchase #4 $137.41   10.446%   $151.7638   $151.76   $151.75   $151.80  
  Purchase #5 $201.94   10.851%   $223.8525   $223.85   $223.85   $223.90  
  Purchase #6 $24.56   5.770%   $25.9771   $25.98   $26.00   $26.00  
  Purchase #7 $123.86   6.769%   $132.2441   $132.24   $132.25   $132.20  
  7 purchase totals = $833.41       $906.9802   $906.97   $906.95   $907.00