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 $217.76   11.122%   $241.9793   $241.98   $242.00   $242.00  
  Purchase #2 $155.57   7.203%   $166.7757   $166.78   $166.80   $166.80  
  Purchase #3 $26.71   9.591%   $29.2718   $29.27   $29.25   $29.30  
  Purchase #4 $250.44   4.712%   $262.2407   $262.24   $262.25   $262.20  
  Purchase #5 $147.76   8.583%   $160.4422   $160.44   $160.45   $160.40  
  Purchase #6 $221.41   3.203%   $228.5018   $228.50   $228.50   $228.50  
  Purchase #7 $192.57   11.179%   $214.0974   $214.10   $214.10   $214.10  
  7 purchase totals = $1,212.22       $1,303.3089   $1,303.31   $1,303.35   $1,303.30