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 $79.62   10.516%   $87.9928   $87.99   $88.00   $88.00  
  Purchase #2 $53.36   6.260%   $56.7003   $56.70   $56.70   $56.70  
  Purchase #3 $165.72   13.408%   $187.9397   $187.94   $187.95   $187.90  
  Purchase #4 $175.92   6.321%   $187.0399   $187.04   $187.05   $187.00  
  Purchase #5 $138.40   4.233%   $144.2585   $144.26   $144.25   $144.30  
  Purchase #6 $65.58   12.675%   $73.8923   $73.89   $73.90   $73.90  
  Purchase #7 $37.32   6.237%   $39.6476   $39.65   $39.65   $39.60  
  7 purchase totals = $715.92       $777.4711   $777.47   $777.50   $777.40