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 $71.67   7.386%   $76.9635   $76.96   $76.95   $77.00  
  Purchase #2 $90.78   4.734%   $95.0775   $95.08   $95.10   $95.10  
  Purchase #3 $162.53   6.418%   $172.9612   $172.96   $172.95   $173.00  
  Purchase #4 $246.88   6.547%   $263.0432   $263.04   $263.05   $263.00  
  Purchase #5 $111.96   7.164%   $119.9808   $119.98   $120.00   $120.00  
  Purchase #6 $136.28   9.227%   $148.8546   $148.85   $148.85   $148.90  
  Purchase #7 $100.64   4.611%   $105.2805   $105.28   $105.30   $105.30  
  7 purchase totals = $920.74       $982.1613   $982.15   $982.20   $982.30