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 $148.62   4.537%   $155.3629   $155.36   $155.35   $155.40  
  Purchase #2 $151.81   9.119%   $165.6536   $165.65   $165.65   $165.70  
  Purchase #3 $177.70   11.864%   $198.7823   $198.78   $198.80   $198.80  
  Purchase #4 $189.66   10.520%   $209.6122   $209.61   $209.60   $209.60  
  Purchase #5 $248.80   4.711%   $260.521   $260.52   $260.50   $260.50  
  Purchase #6 $36.34   11.677%   $40.5834   $40.58   $40.60   $40.60  
  Purchase #7 $121.33   11.441%   $135.2114   $135.21   $135.20   $135.20  
  7 purchase totals = $1,074.26       $1,165.7268   $1,165.71   $1,165.70   $1,165.80