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 $179.78   12.402%   $202.0763   $202.08   $202.10   $202.10  
  Purchase #2 $206.86   6.660%   $220.6369   $220.64   $220.65   $220.60  
  Purchase #3 $154.53   13.289%   $175.0655   $175.07   $175.05   $175.10  
  Purchase #4 $85.84   7.864%   $92.5905   $92.59   $92.60   $92.60  
  Purchase #5 $210.92   12.491%   $237.266   $237.27   $237.25   $237.30  
  Purchase #6 $50.34   6.690%   $53.7077   $53.71   $53.70   $53.70  
  Purchase #7 $74.80   6.693%   $79.8064   $79.81   $79.80   $79.80  
  7 purchase totals = $963.07       $1,061.1493   $1,061.17   $1,061.15   $1,061.20