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 $56.83   5.523%   $59.9687   $59.97   $59.95   $60.00  
  Purchase #2 $165.89   12.439%   $186.5251   $186.53   $186.55   $186.50  
  Purchase #3 $232.85   9.513%   $255.001   $255.00   $255.00   $255.00  
  Purchase #4 $228.25   11.454%   $254.3938   $254.39   $254.40   $254.40  
  Purchase #5 $183.77   13.483%   $208.5477   $208.55   $208.55   $208.50  
  Purchase #6 $101.46   11.651%   $113.2811   $113.28   $113.30   $113.30  
  Purchase #7 $101.69   9.114%   $110.958   $110.96   $110.95   $111.00  
  7 purchase totals = $1,070.74       $1,188.6754   $1,188.68   $1,188.70   $1,188.70