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 $87.26   12.308%   $98   $98.00   $98.00   $98.00  
  Purchase #2 $67.28   9.839%   $73.8997   $73.90   $73.90   $73.90  
  Purchase #3 $195.37   5.322%   $205.7676   $205.77   $205.75   $205.80  
  Purchase #4 $44.34   13.585%   $50.3636   $50.36   $50.35   $50.40  
  Purchase #5 $43.92   11.704%   $49.0604   $49.06   $49.05   $49.10  
  Purchase #6 $139.88   5.230%   $147.1957   $147.20   $147.20   $147.20  
  Purchase #7 $195.76   8.432%   $212.2665   $212.27   $212.25   $212.30  
  7 purchase totals = $773.81       $836.5535   $836.56   $836.50   $836.70