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 $221.52   5.162%   $232.9549   $232.95   $232.95   $233.00  
  Purchase #2 $124.45   10.795%   $137.8844   $137.88   $137.90   $137.90  
  Purchase #3 $227.27   4.655%   $237.8494   $237.85   $237.85   $237.80  
  Purchase #4 $66.66   13.255%   $75.4958   $75.50   $75.50   $75.50  
  Purchase #5 $185.55   13.481%   $210.564   $210.56   $210.55   $210.60  
  Purchase #6 $118.91   3.253%   $122.7781   $122.78   $122.80   $122.80  
  Purchase #7 $187.78   10.241%   $207.0105   $207.01   $207.00   $207.00  
  7 purchase totals = $1,132.14       $1,224.5371   $1,224.53   $1,224.55   $1,224.60