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 $70.84   13.702%   $80.5465   $80.55   $80.55   $80.50  
  Purchase #2 $196.89   5.624%   $207.9631   $207.96   $207.95   $208.00  
  Purchase #3 $244.28   10.731%   $270.4937   $270.49   $270.50   $270.50  
  Purchase #4 $68.40   8.657%   $74.3214   $74.32   $74.30   $74.30  
  Purchase #5 $192.63   4.396%   $201.098   $201.10   $201.10   $201.10  
  Purchase #6 $155.89   3.292%   $161.0219   $161.02   $161.00   $161.00  
  Purchase #7 $94.54   4.247%   $98.5551   $98.56   $98.55   $98.60  
  7 purchase totals = $1,023.47       $1,093.9997   $1,094.00   $1,093.95   $1,094.00