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 $235.74   6.764%   $251.6855   $251.69   $251.70   $251.70  
  Purchase #2 $119.93   8.481%   $130.1013   $130.10   $130.10   $130.10  
  Purchase #3 $152.86   8.795%   $166.304   $166.30   $166.30   $166.30  
  Purchase #4 $37.41   12.518%   $42.093   $42.09   $42.10   $42.10  
  Purchase #5 $52.61   9.196%   $57.448   $57.45   $57.45   $57.40  
  Purchase #6 $201.78   5.522%   $212.9223   $212.92   $212.90   $212.90  
  Purchase #7 $12.54   9.114%   $13.6829   $13.68   $13.70   $13.70  
  7 purchase totals = $812.87       $874.2370   $874.23   $874.25   $874.20