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 $168.42   10.687%   $186.419   $186.42   $186.40   $186.40  
  Purchase #2 $46.27   12.112%   $51.8742   $51.87   $51.85   $51.90  
  Purchase #3 $56.60   11.628%   $63.1814   $63.18   $63.20   $63.20  
  Purchase #4 $245.79   8.247%   $266.0603   $266.06   $266.05   $266.10  
  Purchase #5 $103.46   13.815%   $117.753   $117.75   $117.75   $117.80  
  Purchase #6 $162.83   9.548%   $178.377   $178.38   $178.40   $178.40  
  Purchase #7 $238.96   12.121%   $267.9243   $267.92   $267.90   $267.90  
  7 purchase totals = $1,022.33       $1,131.5892   $1,131.58   $1,131.55   $1,131.70