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 $198.96   13.589%   $225.9967   $226.00   $226.00   $226.00  
  Purchase #2 $103.59   10.854%   $114.8337   $114.83   $114.85   $114.80  
  Purchase #3 $93.28   12.434%   $104.8784   $104.88   $104.90   $104.90  
  Purchase #4 $196.75   3.728%   $204.0848   $204.08   $204.10   $204.10  
  Purchase #5 $155.35   13.418%   $176.1949   $176.19   $176.20   $176.20  
  Purchase #6 $30.51   13.135%   $34.5175   $34.52   $34.50   $34.50  
  Purchase #7 $175.50   7.225%   $188.1799   $188.18   $188.20   $188.20  
  7 purchase totals = $953.94       $1,048.6859   $1,048.68   $1,048.75   $1,048.70