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 $233.72   13.211%   $264.5967   $264.60   $264.60   $264.60  
  Purchase #2 $68.59   13.128%   $77.5945   $77.59   $77.60   $77.60  
  Purchase #3 $76.86   11.842%   $85.9618   $85.96   $85.95   $86.00  
  Purchase #4 $192.46   5.701%   $203.4321   $203.43   $203.45   $203.40  
  Purchase #5 $237.59   7.326%   $254.9958   $255.00   $255.00   $255.00  
  Purchase #6 $65.93   8.139%   $71.296   $71.30   $71.30   $71.30  
  Purchase #7 $243.80   9.123%   $266.0419   $266.04   $266.05   $266.00  
  7 purchase totals = $1,118.95       $1,223.9188   $1,223.92   $1,223.95   $1,223.90