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 $117.96   4.218%   $122.9356   $122.94   $122.95   $122.90  
  Purchase #2 $90.97   5.106%   $95.6149   $95.61   $95.60   $95.60  
  Purchase #3 $77.91   4.865%   $81.7003   $81.70   $81.70   $81.70  
  Purchase #4 $42.69   4.127%   $44.4518   $44.45   $44.45   $44.50  
  Purchase #5 $45.41   8.358%   $49.2054   $49.21   $49.20   $49.20  
  Purchase #6 $184.55   5.123%   $194.0045   $194.00   $194.00   $194.00  
  Purchase #7 $163.95   6.155%   $174.0411   $174.04   $174.05   $174.00  
  7 purchase totals = $723.44       $761.9536   $761.95   $761.95   $761.90