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 $64.35   7.186%   $68.9742   $68.97   $68.95   $69.00  
  Purchase #2 $87.69   7.629%   $94.3799   $94.38   $94.40   $94.40  
  Purchase #3 $103.29   5.316%   $108.7809   $108.78   $108.80   $108.80  
  Purchase #4 $239.58   11.364%   $266.8059   $266.81   $266.80   $266.80  
  Purchase #5 $80.87   10.457%   $89.3266   $89.33   $89.35   $89.30  
  Purchase #6 $139.94   8.152%   $151.3479   $151.35   $151.35   $151.30  
  Purchase #7 $112.59   8.419%   $122.069   $122.07   $122.05   $122.10  
  7 purchase totals = $828.31       $901.6844   $901.69   $901.70   $901.70