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 $207.59   7.482%   $223.1219   $223.12   $223.10   $223.10  
  Purchase #2 $173.28   13.115%   $196.0057   $196.01   $196.00   $196.00  
  Purchase #3 $42.76   8.751%   $46.5019   $46.50   $46.50   $46.50  
  Purchase #4 $236.73   3.861%   $245.8701   $245.87   $245.85   $245.90  
  Purchase #5 $172.36   8.653%   $187.2743   $187.27   $187.25   $187.30  
  Purchase #6 $78.51   11.452%   $87.501   $87.50   $87.50   $87.50  
  Purchase #7 $166.76   6.339%   $177.3309   $177.33   $177.35   $177.30  
  7 purchase totals = $1,077.99       $1,163.6058   $1,163.60   $1,163.55   $1,163.60