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 $59.49   12.620%   $66.9976   $67.00   $67.00   $67.00  
  Purchase #2 $119.86   12.505%   $134.8485   $134.85   $134.85   $134.80  
  Purchase #3 $25.60   8.848%   $27.8651   $27.87   $27.85   $27.90  
  Purchase #4 $176.91   7.143%   $189.5467   $189.55   $189.55   $189.50  
  Purchase #5 $27.80   4.320%   $29.001   $29.00   $29.00   $29.00  
  Purchase #6 $172.93   7.792%   $186.4047   $186.40   $186.40   $186.40  
  Purchase #7 $218.43   6.404%   $232.4183   $232.42   $232.40   $232.40  
  7 purchase totals = $801.02       $867.0819   $867.09   $867.05   $867.00