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 $76.88   3.153%   $79.304   $79.30   $79.30   $79.30  
  Purchase #2 $114.28   6.560%   $121.7768   $121.78   $121.80   $121.80  
  Purchase #3 $95.39   5.659%   $100.7881   $100.79   $100.80   $100.80  
  Purchase #4 $8.66   6.581%   $9.2299   $9.23   $9.25   $9.20  
  Purchase #5 $161.91   12.248%   $181.7407   $181.74   $181.75   $181.70  
  Purchase #6 $147.80   3.585%   $153.0986   $153.10   $153.10   $153.10  
  Purchase #7 $54.75   9.771%   $60.0996   $60.10   $60.10   $60.10  
  7 purchase totals = $659.67       $706.0377   $706.04   $706.10   $706.00