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 $237.80   13.146%   $269.0612   $269.06   $269.05   $269.10  
  Purchase #2 $58.63   11.486%   $65.3642   $65.36   $65.35   $65.40  
  Purchase #3 $50.52   8.237%   $54.6813   $54.68   $54.70   $54.70  
  Purchase #4 $114.80   3.320%   $118.6114   $118.61   $118.60   $118.60  
  Purchase #5 $119.52   3.748%   $123.9996   $124.00   $124.00   $124.00  
  Purchase #6 $214.27   13.511%   $243.22   $243.22   $243.20   $243.20  
  Purchase #7 $156.25   6.686%   $166.6969   $166.70   $166.70   $166.70  
  7 purchase totals = $951.79       $1,041.6346   $1,041.63   $1,041.60   $1,041.70