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 $58.94   12.619%   $66.3776   $66.38   $66.40   $66.40  
  Purchase #2 $72.44   11.320%   $80.6402   $80.64   $80.65   $80.60  
  Purchase #3 $56.86   5.684%   $60.0919   $60.09   $60.10   $60.10  
  Purchase #4 $239.84   12.294%   $269.3259   $269.33   $269.35   $269.30  
  Purchase #5 $10.40   5.589%   $10.9813   $10.98   $11.00   $11.00  
  Purchase #6 $93.25   7.829%   $100.5505   $100.55   $100.55   $100.60  
  Purchase #7 $127.86   5.516%   $134.9128   $134.91   $134.90   $134.90  
  7 purchase totals = $659.59       $722.8802   $722.88   $722.95   $722.90