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 $113.94   8.828%   $123.9986   $124.00   $124.00   $124.00  
  Purchase #2 $210.64   4.644%   $220.4221   $220.42   $220.40   $220.40  
  Purchase #3 $185.46   5.489%   $195.6399   $195.64   $195.65   $195.60  
  Purchase #4 $85.77   9.812%   $94.1858   $94.19   $94.20   $94.20  
  Purchase #5 $131.85   7.236%   $141.3907   $141.39   $141.40   $141.40  
  Purchase #6 $42.39   13.381%   $48.0622   $48.06   $48.05   $48.10  
  Purchase #7 $48.93   6.693%   $52.2049   $52.20   $52.20   $52.20  
  7 purchase totals = $818.98       $875.9042   $875.90   $875.90   $875.90