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 $210.68   5.186%   $221.6059   $221.61   $221.60   $221.60  
  Purchase #2 $56.65   7.631%   $60.973   $60.97   $60.95   $61.00  
  Purchase #3 $111.45   8.288%   $120.687   $120.69   $120.70   $120.70  
  Purchase #4 $92.36   5.112%   $97.0814   $97.08   $97.10   $97.10  
  Purchase #5 $122.76   11.245%   $136.5644   $136.56   $136.55   $136.60  
  Purchase #6 $151.61   9.823%   $166.5027   $166.50   $166.50   $166.50  
  Purchase #7 $235.91   13.230%   $267.1209   $267.12   $267.10   $267.10  
  7 purchase totals = $981.42       $1,070.5353   $1,070.53   $1,070.50   $1,070.60