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 $113.41   9.566%   $124.2588   $124.26   $124.25   $124.30  
  Purchase #2 $139.86   7.395%   $150.2026   $150.20   $150.20   $150.20  
  Purchase #3 $142.81   10.115%   $157.2552   $157.26   $157.25   $157.30  
  Purchase #4 $176.98   11.355%   $197.0761   $197.08   $197.10   $197.10  
  Purchase #5 $116.27   9.222%   $126.9924   $126.99   $127.00   $127.00  
  Purchase #6 $26.70   7.145%   $28.6077   $28.61   $28.60   $28.60  
  Purchase #7 $148.78   11.266%   $165.5416   $165.54   $165.55   $165.50  
  7 purchase totals = $864.81       $949.9344   $949.94   $949.95   $950.00