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 $94.84   12.683%   $106.8686   $106.87   $106.85   $106.90  
  Purchase #2 $119.42   5.803%   $126.3499   $126.35   $126.35   $126.30  
  Purchase #3 $124.95   4.751%   $130.8864   $130.89   $130.90   $130.90  
  Purchase #4 $53.91   6.246%   $57.2772   $57.28   $57.30   $57.30  
  Purchase #5 $226.71   5.411%   $238.9773   $238.98   $239.00   $239.00  
  Purchase #6 $150.44   10.606%   $166.3957   $166.40   $166.40   $166.40  
  Purchase #7 $160.61   10.507%   $177.4853   $177.49   $177.50   $177.50  
  7 purchase totals = $930.88       $1,004.2404   $1,004.26   $1,004.30   $1,004.30