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 $99.71   5.584%   $105.2778   $105.28   $105.30   $105.30  
  Purchase #2 $249.52   4.839%   $261.5943   $261.59   $261.60   $261.60  
  Purchase #3 $235.44   4.194%   $245.3144   $245.31   $245.30   $245.30  
  Purchase #4 $217.77   7.283%   $233.6302   $233.63   $233.65   $233.60  
  Purchase #5 $214.42   12.395%   $240.9974   $241.00   $241.00   $241.00  
  Purchase #6 $167.80   9.825%   $184.2864   $184.29   $184.30   $184.30  
  Purchase #7 $83.29   11.866%   $93.1732   $93.17   $93.15   $93.20  
  7 purchase totals = $1,267.95       $1,364.2737   $1,364.27   $1,364.30   $1,364.30