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 $70.35   8.735%   $76.4951   $76.50   $76.50   $76.50  
  Purchase #2 $124.31   5.547%   $131.2055   $131.21   $131.20   $131.20  
  Purchase #3 $136.90   10.359%   $151.0815   $151.08   $151.10   $151.10  
  Purchase #4 $31.32   6.358%   $33.3113   $33.31   $33.30   $33.30  
  Purchase #5 $169.44   10.303%   $186.8974   $186.90   $186.90   $186.90  
  Purchase #6 $206.59   6.625%   $220.2766   $220.28   $220.30   $220.30  
  Purchase #7 $147.67   9.553%   $161.7769   $161.78   $161.80   $161.80  
  7 purchase totals = $886.58       $961.0443   $961.06   $961.10   $961.10