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 $166.28   12.462%   $187.0018   $187.00   $187.00   $187.00  
  Purchase #2 $163.27   13.347%   $185.0616   $185.06   $185.05   $185.10  
  Purchase #3 $54.87   3.551%   $56.8184   $56.82   $56.80   $56.80  
  Purchase #4 $27.88   7.794%   $30.053   $30.05   $30.05   $30.10  
  Purchase #5 $110.89   12.135%   $124.3465   $124.35   $124.35   $124.30  
  Purchase #6 $84.44   13.359%   $95.7203   $95.72   $95.70   $95.70  
  Purchase #7 $184.46   5.182%   $194.0187   $194.02   $194.00   $194.00  
  7 purchase totals = $792.09       $873.0203   $873.02   $872.95   $873.00