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 $227.72   9.873%   $250.2028   $250.20   $250.20   $250.20  
  Purchase #2 $160.41   4.722%   $167.9846   $167.98   $168.00   $168.00  
  Purchase #3 $57.86   13.271%   $65.5386   $65.54   $65.55   $65.50  
  Purchase #4 $231.25   6.724%   $246.7993   $246.80   $246.80   $246.80  
  Purchase #5 $59.77   7.164%   $64.0519   $64.05   $64.05   $64.10  
  Purchase #6 $105.73   7.272%   $113.4187   $113.42   $113.40   $113.40  
  Purchase #7 $195.97   11.748%   $218.9926   $218.99   $219.00   $219.00  
  7 purchase totals = $1,038.71       $1,126.9885   $1,126.98   $1,127.00   $1,127.00