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 $164.33   12.716%   $185.2262   $185.23   $185.25   $185.20  
  Purchase #2 $247.35   8.178%   $267.5783   $267.58   $267.60   $267.60  
  Purchase #3 $195.74   8.300%   $211.9864   $211.99   $212.00   $212.00  
  Purchase #4 $198.48   13.632%   $225.5368   $225.54   $225.55   $225.50  
  Purchase #5 $169.72   3.138%   $175.0458   $175.05   $175.05   $175.00  
  Purchase #6 $158.72   6.656%   $169.2844   $169.28   $169.30   $169.30  
  Purchase #7 $26.54   7.409%   $28.5063   $28.51   $28.50   $28.50  
  7 purchase totals = $1,160.88       $1,263.1642   $1,263.18   $1,263.25   $1,263.10