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 $178.83   10.714%   $197.9898   $197.99   $198.00   $198.00  
  Purchase #2 $183.78   13.174%   $207.9912   $207.99   $208.00   $208.00  
  Purchase #3 $12.91   11.258%   $14.3634   $14.36   $14.35   $14.40  
  Purchase #4 $101.59   8.464%   $110.1886   $110.19   $110.20   $110.20  
  Purchase #5 $52.26   3.607%   $54.145   $54.15   $54.15   $54.10  
  Purchase #6 $99.76   13.377%   $113.1049   $113.10   $113.10   $113.10  
  Purchase #7 $97.44   13.435%   $110.5311   $110.53   $110.55   $110.50  
  7 purchase totals = $726.57       $808.3140   $808.31   $808.35   $808.30