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 $215.88   6.244%   $229.3595   $229.36   $229.35   $229.40  
  Purchase #2 $44.89   10.777%   $49.7278   $49.73   $49.75   $49.70  
  Purchase #3 $109.56   10.761%   $121.3498   $121.35   $121.35   $121.30  
  Purchase #4 $38.43   13.651%   $43.6761   $43.68   $43.70   $43.70  
  Purchase #5 $225.32   9.616%   $246.9868   $246.99   $247.00   $247.00  
  Purchase #6 $58.79   3.679%   $60.9529   $60.95   $60.95   $61.00  
  Purchase #7 $233.63   12.456%   $262.731   $262.73   $262.75   $262.70  
  7 purchase totals = $926.50       $1,014.7839   $1,014.79   $1,014.85   $1,014.80