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 $198.69   12.231%   $222.9918   $222.99   $223.00   $223.00  
  Purchase #2 $243.25   12.446%   $273.5249   $273.52   $273.50   $273.50  
  Purchase #3 $106.59   7.117%   $114.176   $114.18   $114.20   $114.20  
  Purchase #4 $228.50   9.580%   $250.3903   $250.39   $250.40   $250.40  
  Purchase #5 $87.53   11.644%   $97.722   $97.72   $97.70   $97.70  
  Purchase #6 $154.91   8.492%   $168.065   $168.07   $168.05   $168.10  
  Purchase #7 $215.52   9.863%   $236.7767   $236.78   $236.80   $236.80  
  7 purchase totals = $1,234.99       $1,363.6467   $1,363.65   $1,363.65   $1,363.70