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 $218.28   11.619%   $243.642   $243.64   $243.65   $243.60  
  Purchase #2 $34.33   7.324%   $36.8443   $36.84   $36.85   $36.80  
  Purchase #3 $61.52   9.838%   $67.5723   $67.57   $67.55   $67.60  
  Purchase #4 $127.55   7.638%   $137.2923   $137.29   $137.30   $137.30  
  Purchase #5 $63.57   10.346%   $70.147   $70.15   $70.15   $70.10  
  Purchase #6 $17.45   9.660%   $19.1357   $19.14   $19.15   $19.10  
  Purchase #7 $224.25   7.590%   $241.2706   $241.27   $241.25   $241.30  
  7 purchase totals = $746.95       $815.9042   $815.90   $815.90   $815.80