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 $213.52   8.666%   $232.0236   $232.02   $232.00   $232.00  
  Purchase #2 $77.27   3.541%   $80.0061   $80.01   $80.00   $80.00  
  Purchase #3 $98.37   7.681%   $105.9258   $105.93   $105.95   $105.90  
  Purchase #4 $76.41   13.315%   $86.584   $86.58   $86.60   $86.60  
  Purchase #5 $187.52   12.833%   $211.5844   $211.58   $211.60   $211.60  
  Purchase #6 $215.52   13.677%   $244.9967   $245.00   $245.00   $245.00  
  Purchase #7 $29.84   10.718%   $33.0383   $33.04   $33.05   $33.00  
  7 purchase totals = $898.45       $994.1589   $994.16   $994.20   $994.10