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 $214.82   11.716%   $239.9883   $239.99   $240.00   $240.00  
  Purchase #2 $211.72   6.737%   $225.9836   $225.98   $226.00   $226.00  
  Purchase #3 $226.53   12.191%   $254.1463   $254.15   $254.15   $254.10  
  Purchase #4 $232.71   4.506%   $243.1959   $243.20   $243.20   $243.20  
  Purchase #5 $30.65   6.176%   $32.5429   $32.54   $32.55   $32.50  
  Purchase #6 $105.57   9.873%   $115.9929   $115.99   $116.00   $116.00  
  Purchase #7 $19.95   12.408%   $22.4254   $22.43   $22.45   $22.40  
  7 purchase totals = $1,041.95       $1,134.2753   $1,134.28   $1,134.35   $1,134.20