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 $212.52   3.124%   $219.1591   $219.16   $219.15   $219.20  
  Purchase #2 $61.74   9.633%   $67.6874   $67.69   $67.70   $67.70  
  Purchase #3 $74.58   6.275%   $79.2599   $79.26   $79.25   $79.30  
  Purchase #4 $162.55   5.267%   $171.1115   $171.11   $171.10   $171.10  
  Purchase #5 $6.52   4.400%   $6.8069   $6.81   $6.80   $6.80  
  Purchase #6 $53.97   8.304%   $58.4517   $58.45   $58.45   $58.50  
  Purchase #7 $154.48   11.217%   $171.808   $171.81   $171.80   $171.80  
  7 purchase totals = $726.36       $774.2845   $774.29   $774.25   $774.40