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 $215.26   10.109%   $237.0206   $237.02   $237.00   $237.00  
  Purchase #2 $144.84   4.248%   $150.9928   $150.99   $151.00   $151.00  
  Purchase #3 $61.83   3.648%   $64.0856   $64.09   $64.10   $64.10  
  Purchase #4 $211.95   4.216%   $220.8858   $220.89   $220.90   $220.90  
  Purchase #5 $153.28   13.409%   $173.8333   $173.83   $173.85   $173.80  
  Purchase #6 $152.52   4.573%   $159.4947   $159.49   $159.50   $159.50  
  Purchase #7 $128.44   4.546%   $134.2789   $134.28   $134.30   $134.30  
  7 purchase totals = $1,068.12       $1,140.5917   $1,140.59   $1,140.65   $1,140.60