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 $228.96   5.874%   $242.4091   $242.41   $242.40   $242.40  
  Purchase #2 $242.90   3.315%   $250.9521   $250.95   $250.95   $251.00  
  Purchase #3 $169.29   4.548%   $176.9893   $176.99   $177.00   $177.00  
  Purchase #4 $106.93   13.189%   $121.033   $121.03   $121.05   $121.00  
  Purchase #5 $96.91   6.362%   $103.0754   $103.08   $103.10   $103.10  
  Purchase #6 $68.82   7.114%   $73.7159   $73.72   $73.70   $73.70  
  Purchase #7 $24.39   11.133%   $27.1053   $27.11   $27.10   $27.10  
  7 purchase totals = $938.20       $995.2801   $995.29   $995.30   $995.30