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 $46.91   9.420%   $51.3289   $51.33   $51.35   $51.30  
  Purchase #2 $114.49   10.719%   $126.7622   $126.76   $126.75   $126.80  
  Purchase #3 $66.48   10.255%   $73.2975   $73.30   $73.30   $73.30  
  Purchase #4 $191.40   5.864%   $202.6237   $202.62   $202.60   $202.60  
  Purchase #5 $123.78   10.647%   $136.9589   $136.96   $136.95   $137.00  
  Purchase #6 $170.33   3.839%   $176.869   $176.87   $176.85   $176.90  
  Purchase #7 $59.62   12.852%   $67.2824   $67.28   $67.30   $67.30  
  7 purchase totals = $773.01       $835.1226   $835.12   $835.10   $835.20