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 $92.80   7.855%   $100.0894   $100.09   $100.10   $100.10  
  Purchase #2 $175.81   5.365%   $185.2422   $185.24   $185.25   $185.20  
  Purchase #3 $112.51   8.113%   $121.6379   $121.64   $121.65   $121.60  
  Purchase #4 $22.81   7.642%   $24.5531   $24.55   $24.55   $24.60  
  Purchase #5 $171.26   12.839%   $193.2481   $193.25   $193.25   $193.20  
  Purchase #6 $218.30   3.204%   $225.2943   $225.29   $225.30   $225.30  
  Purchase #7 $70.65   9.522%   $77.3773   $77.38   $77.40   $77.40  
  7 purchase totals = $864.14       $927.4423   $927.44   $927.50   $927.40