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 $202.52   10.873%   $224.54   $224.54   $224.55   $224.50  
  Purchase #2 $40.91   6.814%   $43.6976   $43.70   $43.70   $43.70  
  Purchase #3 $34.45   13.366%   $39.0546   $39.05   $39.05   $39.10  
  Purchase #4 $248.71   7.572%   $267.5423   $267.54   $267.55   $267.50  
  Purchase #5 $156.64   9.168%   $171.0008   $171.00   $171.00   $171.00  
  Purchase #6 $22.78   5.621%   $24.0605   $24.06   $24.05   $24.10  
  Purchase #7 $115.66   7.123%   $123.8985   $123.90   $123.90   $123.90  
  7 purchase totals = $821.67       $893.7943   $893.79   $893.80   $893.80