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 $213.72   11.246%   $237.755   $237.76   $237.75   $237.80  
  Purchase #2 $5.30   12.756%   $5.9761   $5.98   $6.00   $6.00  
  Purchase #3 $150.83   10.512%   $166.6852   $166.69   $166.70   $166.70  
  Purchase #4 $44.27   11.282%   $49.2645   $49.26   $49.25   $49.30  
  Purchase #5 $127.92   5.505%   $134.962   $134.96   $134.95   $135.00  
  Purchase #6 $64.99   3.863%   $67.5006   $67.50   $67.50   $67.50  
  Purchase #7 $153.48   9.232%   $167.6493   $167.65   $167.65   $167.60  
  7 purchase totals = $760.51       $829.7927   $829.80   $829.80   $829.90