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 $62.38   5.203%   $65.6256   $65.63   $65.65   $65.60  
  Purchase #2 $35.97   6.383%   $38.266   $38.27   $38.25   $38.30  
  Purchase #3 $79.93   10.539%   $88.3538   $88.35   $88.35   $88.40  
  Purchase #4 $199.88   8.492%   $216.8538   $216.85   $216.85   $216.90  
  Purchase #5 $207.93   8.401%   $225.3982   $225.40   $225.40   $225.40  
  Purchase #6 $216.61   13.495%   $245.8415   $245.84   $245.85   $245.80  
  Purchase #7 $71.80   12.372%   $80.6831   $80.68   $80.70   $80.70  
  7 purchase totals = $874.50       $961.0220   $961.02   $961.05   $961.10