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 $120.67   10.268%   $133.0604   $133.06   $133.05   $133.10  
  Purchase #2 $168.28   13.174%   $190.4492   $190.45   $190.45   $190.40  
  Purchase #3 $118.70   4.425%   $123.9525   $123.95   $123.95   $124.00  
  Purchase #4 $21.28   13.801%   $24.2169   $24.22   $24.20   $24.20  
  Purchase #5 $190.77   8.867%   $207.6856   $207.69   $207.70   $207.70  
  Purchase #6 $131.34   12.367%   $147.5828   $147.58   $147.60   $147.60  
  Purchase #7 $209.78   4.681%   $219.5998   $219.60   $219.60   $219.60  
  7 purchase totals = $960.82       $1,046.5472   $1,046.55   $1,046.55   $1,046.60