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 $207.76   8.142%   $224.6758   $224.68   $224.70   $224.70  
  Purchase #2 $63.30   8.524%   $68.6957   $68.70   $68.70   $68.70  
  Purchase #3 $112.71   4.729%   $118.0401   $118.04   $118.05   $118.00  
  Purchase #4 $41.94   5.316%   $44.1695   $44.17   $44.15   $44.20  
  Purchase #5 $74.29   11.873%   $83.1105   $83.11   $83.10   $83.10  
  Purchase #6 $66.64   10.508%   $73.6425   $73.64   $73.65   $73.60  
  Purchase #7 $153.60   13.405%   $174.1901   $174.19   $174.20   $174.20  
  7 purchase totals = $720.24       $786.5242   $786.53   $786.55   $786.50