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 $113.75   5.110%   $119.5626   $119.56   $119.55   $119.60  
  Purchase #2 $135.52   6.619%   $144.4901   $144.49   $144.50   $144.50  
  Purchase #3 $161.27   7.601%   $173.5281   $173.53   $173.55   $173.50  
  Purchase #4 $211.85   8.710%   $230.3021   $230.30   $230.30   $230.30  
  Purchase #5 $52.86   9.509%   $57.8865   $57.89   $57.90   $57.90  
  Purchase #6 $225.35   9.658%   $247.1143   $247.11   $247.10   $247.10  
  Purchase #7 $90.58   5.149%   $95.244   $95.24   $95.25   $95.20  
  7 purchase totals = $991.18       $1,068.1277   $1,068.12   $1,068.15   $1,068.10