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 $54.46   3.791%   $56.5246   $56.52   $56.50   $56.50  
  Purchase #2 $58.60   3.421%   $60.6047   $60.60   $60.60   $60.60  
  Purchase #3 $190.42   9.504%   $208.5175   $208.52   $208.50   $208.50  
  Purchase #4 $126.71   11.781%   $141.6377   $141.64   $141.65   $141.60  
  Purchase #5 $126.40   8.280%   $136.8659   $136.87   $136.85   $136.90  
  Purchase #6 $173.92   6.771%   $185.6961   $185.70   $185.70   $185.70  
  Purchase #7 $163.62   5.119%   $171.9957   $172.00   $172.00   $172.00  
  7 purchase totals = $894.13       $961.8422   $961.85   $961.80   $961.80