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 $115.58   9.466%   $126.5208   $126.52   $126.50   $126.50  
  Purchase #2 $232.67   13.213%   $263.4127   $263.41   $263.40   $263.40  
  Purchase #3 $86.45   7.564%   $92.9891   $92.99   $93.00   $93.00  
  Purchase #4 $164.37   10.376%   $181.425   $181.43   $181.45   $181.40  
  Purchase #5 $151.66   13.553%   $172.2145   $172.21   $172.20   $172.20  
  Purchase #6 $104.66   6.161%   $111.1081   $111.11   $111.10   $111.10  
  Purchase #7 $144.36   6.494%   $153.7347   $153.73   $153.75   $153.70  
  7 purchase totals = $999.75       $1,101.4049   $1,101.40   $1,101.40   $1,101.30