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 $163.26   12.664%   $183.9352   $183.94   $183.95   $183.90  
  Purchase #2 $26.51   8.641%   $28.8007   $28.80   $28.80   $28.80  
  Purchase #3 $102.77   10.838%   $113.9082   $113.91   $113.90   $113.90  
  Purchase #4 $118.26   11.202%   $131.5075   $131.51   $131.50   $131.50  
  Purchase #5 $202.29   11.299%   $225.1467   $225.15   $225.15   $225.10  
  Purchase #6 $168.82   3.278%   $174.3539   $174.35   $174.35   $174.40  
  Purchase #7 $44.67   5.245%   $47.0129   $47.01   $47.00   $47.00  
  7 purchase totals = $826.58       $904.6651   $904.67   $904.65   $904.60