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 $48.43   10.542%   $53.5355   $53.54   $53.55   $53.50  
  Purchase #2 $246.64   12.328%   $277.0458   $277.05   $277.05   $277.00  
  Purchase #3 $39.88   12.414%   $44.8307   $44.83   $44.85   $44.80  
  Purchase #4 $126.60   6.210%   $134.4619   $134.46   $134.45   $134.50  
  Purchase #5 $110.85   9.615%   $121.5082   $121.51   $121.50   $121.50  
  Purchase #6 $13.81   13.301%   $15.6469   $15.65   $15.65   $15.60  
  Purchase #7 $109.25   9.299%   $119.4092   $119.41   $119.40   $119.40  
  7 purchase totals = $695.46       $766.4382   $766.45   $766.45   $766.30