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 $54.66   10.317%   $60.2993   $60.30   $60.30   $60.30  
  Purchase #2 $70.39   6.289%   $74.8168   $74.82   $74.80   $74.80  
  Purchase #3 $33.90   13.285%   $38.4036   $38.40   $38.40   $38.40  
  Purchase #4 $43.36   3.786%   $45.0016   $45.00   $45.00   $45.00  
  Purchase #5 $233.52   12.640%   $263.0369   $263.04   $263.05   $263.00  
  Purchase #6 $229.94   12.311%   $258.2479   $258.25   $258.25   $258.20  
  Purchase #7 $104.81   9.374%   $114.6349   $114.63   $114.65   $114.60  
  7 purchase totals = $770.58       $854.4410   $854.44   $854.45   $854.30