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 $38.77   11.838%   $43.3596   $43.36   $43.35   $43.40  
  Purchase #2 $248.50   8.587%   $269.8387   $269.84   $269.85   $269.80  
  Purchase #3 $65.67   4.786%   $68.813   $68.81   $68.80   $68.80  
  Purchase #4 $210.53   11.605%   $234.962   $234.96   $234.95   $235.00  
  Purchase #5 $196.32   11.826%   $219.5368   $219.54   $219.55   $219.50  
  Purchase #6 $89.56   7.610%   $96.3755   $96.38   $96.40   $96.40  
  Purchase #7 $214.63   13.721%   $244.0794   $244.08   $244.10   $244.10  
  7 purchase totals = $1,063.98       $1,176.9650   $1,176.97   $1,177.00   $1,177.00