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 $202.44   7.821%   $218.2728   $218.27   $218.25   $218.30  
  Purchase #2 $224.46   12.671%   $252.9013   $252.90   $252.90   $252.90  
  Purchase #3 $235.85   4.842%   $247.2699   $247.27   $247.25   $247.30  
  Purchase #4 $98.66   7.785%   $106.3407   $106.34   $106.35   $106.30  
  Purchase #5 $218.91   13.328%   $248.0863   $248.09   $248.10   $248.10  
  Purchase #6 $142.66   8.846%   $155.2797   $155.28   $155.30   $155.30  
  Purchase #7 $8.27   6.268%   $8.7884   $8.79   $8.80   $8.80  
  7 purchase totals = $1,131.25       $1,236.9391   $1,236.94   $1,236.95   $1,237.00