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 $160.80   9.259%   $175.6885   $175.69   $175.70   $175.70  
  Purchase #2 $46.91   6.146%   $49.7931   $49.79   $49.80   $49.80  
  Purchase #3 $139.99   4.788%   $146.6927   $146.69   $146.70   $146.70  
  Purchase #4 $43.62   4.522%   $45.5925   $45.59   $45.60   $45.60  
  Purchase #5 $109.90   6.869%   $117.449   $117.45   $117.45   $117.40  
  Purchase #6 $122.56   10.323%   $135.2119   $135.21   $135.20   $135.20  
  Purchase #7 $132.74   9.680%   $145.5892   $145.59   $145.60   $145.60  
  7 purchase totals = $756.52       $816.0169   $816.01   $816.05   $816.00