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 $239.33   11.572%   $267.0253   $267.03   $267.05   $267.00  
  Purchase #2 $165.94   4.801%   $173.9068   $173.91   $173.90   $173.90  
  Purchase #3 $168.45   7.652%   $181.3398   $181.34   $181.35   $181.30  
  Purchase #4 $62.59   4.669%   $65.5123   $65.51   $65.50   $65.50  
  Purchase #5 $238.95   12.119%   $267.9084   $267.91   $267.90   $267.90  
  Purchase #6 $138.87   3.766%   $144.0998   $144.10   $144.10   $144.10  
  Purchase #7 $166.86   3.239%   $172.2646   $172.26   $172.25   $172.30  
  7 purchase totals = $1,180.99       $1,272.0570   $1,272.06   $1,272.05   $1,272.00