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 $16.54   8.476%   $17.9419   $17.94   $17.95   $17.90  
  Purchase #2 $150.79   13.736%   $171.5025   $171.50   $171.50   $171.50  
  Purchase #3 $243.95   3.391%   $252.2223   $252.22   $252.20   $252.20  
  Purchase #4 $176.67   12.131%   $198.1018   $198.10   $198.10   $198.10  
  Purchase #5 $128.59   11.839%   $143.8138   $143.81   $143.80   $143.80  
  Purchase #6 $73.39   10.473%   $81.0761   $81.08   $81.10   $81.10  
  Purchase #7 $21.60   4.335%   $22.5364   $22.54   $22.55   $22.50  
  7 purchase totals = $811.53       $887.1948   $887.19   $887.20   $887.10