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 $150.33   11.319%   $167.3459   $167.35   $167.35   $167.30  
  Purchase #2 $208.58   4.176%   $217.2903   $217.29   $217.30   $217.30  
  Purchase #3 $121.93   3.746%   $126.4975   $126.50   $126.50   $126.50  
  Purchase #4 $185.27   9.598%   $203.0522   $203.05   $203.05   $203.10  
  Purchase #5 $88.57   8.124%   $95.7654   $95.77   $95.75   $95.80  
  Purchase #6 $235.85   5.107%   $247.8949   $247.89   $247.90   $247.90  
  Purchase #7 $140.69   12.570%   $158.3747   $158.37   $158.35   $158.40  
  7 purchase totals = $1,131.22       $1,216.2209   $1,216.22   $1,216.20   $1,216.30