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 $184.55   9.461%   $202.0103   $202.01   $202.00   $202.00  
  Purchase #2 $206.62   8.149%   $223.4575   $223.46   $223.45   $223.50  
  Purchase #3 $167.64   3.767%   $173.955   $173.96   $173.95   $174.00  
  Purchase #4 $38.81   7.186%   $41.5989   $41.60   $41.60   $41.60  
  Purchase #5 $30.81   9.327%   $33.6836   $33.68   $33.70   $33.70  
  Purchase #6 $73.53   5.732%   $77.7447   $77.74   $77.75   $77.70  
  Purchase #7 $235.82   3.558%   $244.2105   $244.21   $244.20   $244.20  
  7 purchase totals = $937.78       $996.6605   $996.66   $996.65   $996.70