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 $50.86   10.751%   $56.328   $56.33   $56.35   $56.30  
  Purchase #2 $208.77   6.233%   $221.7826   $221.78   $221.80   $221.80  
  Purchase #3 $77.66   3.131%   $80.0915   $80.09   $80.10   $80.10  
  Purchase #4 $214.36   7.496%   $230.4284   $230.43   $230.45   $230.40  
  Purchase #5 $99.33   11.559%   $110.8116   $110.81   $110.80   $110.80  
  Purchase #6 $235.62   4.106%   $245.2946   $245.29   $245.30   $245.30  
  Purchase #7 $80.59   13.446%   $91.4261   $91.43   $91.45   $91.40  
  7 purchase totals = $967.19       $1,036.1628   $1,036.16   $1,036.25   $1,036.10