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 $168.66   10.287%   $186.0101   $186.01   $186.00   $186.00  
  Purchase #2 $159.66   13.726%   $181.5749   $181.57   $181.55   $181.60  
  Purchase #3 $198.28   13.149%   $224.3518   $224.35   $224.35   $224.40  
  Purchase #4 $216.76   13.222%   $245.42   $245.42   $245.40   $245.40  
  Purchase #5 $38.26   6.740%   $40.8387   $40.84   $40.85   $40.80  
  Purchase #6 $56.45   13.504%   $64.073   $64.07   $64.05   $64.10  
  Purchase #7 $175.95   7.268%   $188.738   $188.74   $188.75   $188.70  
  7 purchase totals = $1,014.02       $1,131.0065   $1,131.00   $1,130.95   $1,131.00