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 $198.88   11.668%   $222.0853   $222.09   $222.10   $222.10  
  Purchase #2 $190.30   8.224%   $205.9503   $205.95   $205.95   $206.00  
  Purchase #3 $60.74   6.228%   $64.5229   $64.52   $64.50   $64.50  
  Purchase #4 $86.80   10.770%   $96.1484   $96.15   $96.15   $96.10  
  Purchase #5 $106.71   11.258%   $118.7234   $118.72   $118.70   $118.70  
  Purchase #6 $196.39   5.163%   $206.5296   $206.53   $206.55   $206.50  
  Purchase #7 $122.74   6.475%   $130.6874   $130.69   $130.70   $130.70  
  7 purchase totals = $962.56       $1,044.6473   $1,044.65   $1,044.65   $1,044.60