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 $171.59   5.841%   $181.6126   $181.61   $181.60   $181.60  
  Purchase #2 $154.29   4.479%   $161.2006   $161.20   $161.20   $161.20  
  Purchase #3 $197.86   5.123%   $207.9964   $208.00   $208.00   $208.00  
  Purchase #4 $232.28   7.269%   $249.1644   $249.16   $249.15   $249.20  
  Purchase #5 $151.49   10.581%   $167.5192   $167.52   $167.50   $167.50  
  Purchase #6 $46.71   9.330%   $51.068   $51.07   $51.05   $51.10  
  Purchase #7 $172.54   3.278%   $178.1959   $178.20   $178.20   $178.20  
  7 purchase totals = $1,126.76       $1,196.7571   $1,196.76   $1,196.70   $1,196.80