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 $5.97   4.434%   $6.2347   $6.23   $6.25   $6.20  
  Purchase #2 $65.52   5.497%   $69.1216   $69.12   $69.10   $69.10  
  Purchase #3 $61.31   3.730%   $63.5969   $63.60   $63.60   $63.60  
  Purchase #4 $203.95   9.687%   $223.7066   $223.71   $223.70   $223.70  
  Purchase #5 $59.29   8.834%   $64.5277   $64.53   $64.55   $64.50  
  Purchase #6 $127.91   7.558%   $137.5774   $137.58   $137.60   $137.60  
  Purchase #7 $109.80   13.464%   $124.5835   $124.58   $124.60   $124.60  
  7 purchase totals = $633.75       $689.3484   $689.35   $689.40   $689.30