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 $103.79   13.726%   $118.0362   $118.04   $118.05   $118.00  
  Purchase #2 $109.51   11.552%   $122.1606   $122.16   $122.15   $122.20  
  Purchase #3 $220.53   3.745%   $228.7888   $228.79   $228.80   $228.80  
  Purchase #4 $44.73   13.634%   $50.8285   $50.83   $50.85   $50.80  
  Purchase #5 $189.87   9.698%   $208.2836   $208.28   $208.30   $208.30  
  Purchase #6 $145.56   5.874%   $154.1102   $154.11   $154.10   $154.10  
  Purchase #7 $161.75   5.849%   $171.2108   $171.21   $171.20   $171.20  
  7 purchase totals = $975.74       $1,053.4187   $1,053.42   $1,053.45   $1,053.40