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 $118.83   6.733%   $126.8308   $126.83   $126.85   $126.80  
  Purchase #2 $41.98   13.779%   $47.7644   $47.76   $47.75   $47.80  
  Purchase #3 $114.57   3.847%   $118.9775   $118.98   $119.00   $119.00  
  Purchase #4 $205.42   3.801%   $213.228   $213.23   $213.25   $213.20  
  Purchase #5 $114.96   4.620%   $120.2712   $120.27   $120.25   $120.30  
  Purchase #6 $46.28   9.512%   $50.6822   $50.68   $50.70   $50.70  
  Purchase #7 $203.45   11.239%   $226.3157   $226.32   $226.30   $226.30  
  7 purchase totals = $845.49       $904.0698   $904.07   $904.10   $904.10