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 $115.76   6.703%   $123.5194   $123.52   $123.50   $123.50  
  Purchase #2 $244.88   8.606%   $265.9544   $265.95   $265.95   $266.00  
  Purchase #3 $46.49   11.158%   $51.6774   $51.68   $51.70   $51.70  
  Purchase #4 $157.35   5.691%   $166.3048   $166.30   $166.30   $166.30  
  Purchase #5 $223.97   3.417%   $231.6231   $231.62   $231.60   $231.60  
  Purchase #6 $106.36   13.836%   $121.076   $121.08   $121.10   $121.10  
  Purchase #7 $204.55   9.653%   $224.2952   $224.30   $224.30   $224.30  
  7 purchase totals = $1,099.36       $1,184.4503   $1,184.45   $1,184.45   $1,184.50