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 $158.67   11.327%   $176.6426   $176.64   $176.65   $176.60  
  Purchase #2 $149.89   8.357%   $162.4163   $162.42   $162.40   $162.40  
  Purchase #3 $83.45   4.465%   $87.176   $87.18   $87.20   $87.20  
  Purchase #4 $179.99   5.624%   $190.1126   $190.11   $190.10   $190.10  
  Purchase #5 $43.69   10.269%   $48.1765   $48.18   $48.20   $48.20  
  Purchase #6 $22.56   6.292%   $23.9795   $23.98   $24.00   $24.00  
  Purchase #7 $235.39   11.742%   $263.0295   $263.03   $263.05   $263.00  
  7 purchase totals = $873.64       $951.5330   $951.54   $951.60   $951.50