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 $242.76   7.546%   $261.0787   $261.08   $261.10   $261.10  
  Purchase #2 $189.48   7.755%   $204.1742   $204.17   $204.15   $204.20  
  Purchase #3 $6.26   9.448%   $6.8514   $6.85   $6.85   $6.90  
  Purchase #4 $77.41   7.562%   $83.2637   $83.26   $83.25   $83.30  
  Purchase #5 $108.45   5.735%   $114.6696   $114.67   $114.65   $114.70  
  Purchase #6 $175.40   3.686%   $181.8652   $181.87   $181.85   $181.90  
  Purchase #7 $150.35   11.434%   $167.541   $167.54   $167.55   $167.50  
  7 purchase totals = $950.11       $1,019.4438   $1,019.44   $1,019.40   $1,019.60