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 $29.97   12.783%   $33.8011   $33.80   $33.80   $33.80  
  Purchase #2 $194.69   5.411%   $205.2247   $205.22   $205.20   $205.20  
  Purchase #3 $161.52   9.316%   $176.5672   $176.57   $176.55   $176.60  
  Purchase #4 $237.40   11.845%   $265.52   $265.52   $265.50   $265.50  
  Purchase #5 $25.56   11.439%   $28.4838   $28.48   $28.50   $28.50  
  Purchase #6 $83.25   11.864%   $93.1268   $93.13   $93.15   $93.10  
  Purchase #7 $206.97   3.284%   $213.7669   $213.77   $213.75   $213.80  
  7 purchase totals = $939.36       $1,016.4905   $1,016.49   $1,016.45   $1,016.50