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 $94.39   8.110%   $102.045   $102.05   $102.05   $102.00  
  Purchase #2 $128.29   10.675%   $141.985   $141.99   $142.00   $142.00  
  Purchase #3 $8.44   7.162%   $9.0445   $9.04   $9.05   $9.00  
  Purchase #4 $134.74   11.255%   $149.905   $149.91   $149.90   $149.90  
  Purchase #5 $44.26   13.856%   $50.3927   $50.39   $50.40   $50.40  
  Purchase #6 $166.49   13.533%   $189.0211   $189.02   $189.00   $189.00  
  Purchase #7 $117.27   12.293%   $131.686   $131.69   $131.70   $131.70  
  7 purchase totals = $693.88       $774.0793   $774.09   $774.10   $774.00