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 $116.27   6.844%   $124.2275   $124.23   $124.25   $124.20  
  Purchase #2 $8.33   3.691%   $8.6375   $8.64   $8.65   $8.60  
  Purchase #3 $89.80   11.270%   $99.9205   $99.92   $99.90   $99.90  
  Purchase #4 $185.77   7.746%   $200.1597   $200.16   $200.15   $200.20  
  Purchase #5 $217.94   10.784%   $241.4426   $241.44   $241.45   $241.40  
  Purchase #6 $229.47   7.582%   $246.8684   $246.87   $246.85   $246.90  
  Purchase #7 $96.66   6.349%   $102.7969   $102.80   $102.80   $102.80  
  7 purchase totals = $944.24       $1,024.0531   $1,024.06   $1,024.05   $1,024.00