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 $49.85   13.874%   $56.7662   $56.77   $56.75   $56.80  
  Purchase #2 $185.59   11.625%   $207.1648   $207.16   $207.15   $207.20  
  Purchase #3 $59.83   4.361%   $62.4392   $62.44   $62.45   $62.40  
  Purchase #4 $220.84   5.124%   $232.1558   $232.16   $232.15   $232.20  
  Purchase #5 $91.50   5.612%   $96.635   $96.64   $96.65   $96.60  
  Purchase #6 $44.43   13.144%   $50.2699   $50.27   $50.25   $50.30  
  Purchase #7 $136.72   7.591%   $147.0984   $147.10   $147.10   $147.10  
  7 purchase totals = $788.76       $852.5293   $852.54   $852.50   $852.60