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 $166.46   8.536%   $180.669   $180.67   $180.65   $180.70  
  Purchase #2 $86.53   7.858%   $93.3295   $93.33   $93.35   $93.30  
  Purchase #3 $95.59   7.866%   $103.1091   $103.11   $103.10   $103.10  
  Purchase #4 $198.77   7.235%   $213.151   $213.15   $213.15   $213.20  
  Purchase #5 $231.98   12.406%   $260.7594   $260.76   $260.75   $260.80  
  Purchase #6 $240.64   10.244%   $265.2912   $265.29   $265.30   $265.30  
  Purchase #7 $134.56   9.443%   $147.2665   $147.27   $147.25   $147.30  
  7 purchase totals = $1,154.53       $1,263.5757   $1,263.58   $1,263.55   $1,263.70