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 $67.58   7.802%   $72.8526   $72.85   $72.85   $72.90  
  Purchase #2 $239.66   13.574%   $272.1914   $272.19   $272.20   $272.20  
  Purchase #3 $201.96   13.202%   $228.6228   $228.62   $228.60   $228.60  
  Purchase #4 $116.59   8.227%   $126.1819   $126.18   $126.20   $126.20  
  Purchase #5 $240.81   10.568%   $266.2588   $266.26   $266.25   $266.30  
  Purchase #6 $60.32   7.575%   $64.8892   $64.89   $64.90   $64.90  
  Purchase #7 $13.55   7.658%   $14.5877   $14.59   $14.60   $14.60  
  7 purchase totals = $940.47       $1,045.5844   $1,045.58   $1,045.60   $1,045.70