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 $64.67   6.359%   $68.7824   $68.78   $68.80   $68.80  
  Purchase #2 $248.95   9.710%   $273.123   $273.12   $273.10   $273.10  
  Purchase #3 $186.87   3.648%   $193.687   $193.69   $193.70   $193.70  
  Purchase #4 $41.97   4.413%   $43.8221   $43.82   $43.80   $43.80  
  Purchase #5 $127.91   6.474%   $136.1909   $136.19   $136.20   $136.20  
  Purchase #6 $114.54   11.490%   $127.7006   $127.70   $127.70   $127.70  
  Purchase #7 $170.74   9.716%   $187.3291   $187.33   $187.35   $187.30  
  7 purchase totals = $955.65       $1,030.6351   $1,030.63   $1,030.65   $1,030.60