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 $154.99   7.566%   $166.7165   $166.72   $166.70   $166.70  
  Purchase #2 $107.51   6.592%   $114.5971   $114.60   $114.60   $114.60  
  Purchase #3 $240.71   5.277%   $253.4123   $253.41   $253.40   $253.40  
  Purchase #4 $203.28   4.340%   $212.1024   $212.10   $212.10   $212.10  
  Purchase #5 $58.50   9.463%   $64.0359   $64.04   $64.05   $64.00  
  Purchase #6 $196.63   3.115%   $202.755   $202.76   $202.75   $202.80  
  Purchase #7 $132.70   4.808%   $139.0802   $139.08   $139.10   $139.10  
  7 purchase totals = $1,094.32       $1,152.6994   $1,152.71   $1,152.70   $1,152.70