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 $159.71   13.319%   $180.9818   $180.98   $181.00   $181.00  
  Purchase #2 $117.68   4.749%   $123.2686   $123.27   $123.25   $123.30  
  Purchase #3 $210.83   11.619%   $235.3263   $235.33   $235.35   $235.30  
  Purchase #4 $104.25   12.299%   $117.0717   $117.07   $117.05   $117.10  
  Purchase #5 $214.67   7.797%   $231.4078   $231.41   $231.40   $231.40  
  Purchase #6 $250.30   6.673%   $267.0025   $267.00   $267.00   $267.00  
  Purchase #7 $126.53   10.835%   $140.2395   $140.24   $140.25   $140.20  
  7 purchase totals = $1,183.97       $1,295.2982   $1,295.30   $1,295.30   $1,295.30