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 $213.64   7.469%   $229.5968   $229.60   $229.60   $229.60  
  Purchase #2 $92.60   4.427%   $96.6994   $96.70   $96.70   $96.70  
  Purchase #3 $58.50   12.376%   $65.74   $65.74   $65.75   $65.70  
  Purchase #4 $91.53   6.210%   $97.214   $97.21   $97.20   $97.20  
  Purchase #5 $105.76   5.791%   $111.8846   $111.88   $111.90   $111.90  
  Purchase #6 $248.57   13.566%   $282.291   $282.29   $282.30   $282.30  
  Purchase #7 $100.40   5.113%   $105.5335   $105.53   $105.55   $105.50  
  7 purchase totals = $911.00       $988.9593   $988.95   $989.00   $988.90