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 $90.85   8.484%   $98.5577   $98.56   $98.55   $98.60  
  Purchase #2 $51.88   11.716%   $57.9583   $57.96   $57.95   $58.00  
  Purchase #3 $50.59   4.747%   $52.9915   $52.99   $53.00   $53.00  
  Purchase #4 $183.83   8.753%   $199.9206   $199.92   $199.90   $199.90  
  Purchase #5 $30.53   3.411%   $31.5714   $31.57   $31.55   $31.60  
  Purchase #6 $86.56   8.869%   $94.237   $94.24   $94.25   $94.20  
  Purchase #7 $81.95   10.723%   $90.7375   $90.74   $90.75   $90.70  
  7 purchase totals = $576.19       $625.9740   $625.98   $625.95   $626.00