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 $65.75   5.236%   $69.1927   $69.19   $69.20   $69.20  
  Purchase #2 $181.90   3.355%   $188.0027   $188.00   $188.00   $188.00  
  Purchase #3 $162.51   11.159%   $180.6445   $180.64   $180.65   $180.60  
  Purchase #4 $237.99   11.571%   $265.5278   $265.53   $265.55   $265.50  
  Purchase #5 $232.53   11.578%   $259.4523   $259.45   $259.45   $259.50  
  Purchase #6 $226.64   11.434%   $252.554   $252.55   $252.55   $252.60  
  Purchase #7 $194.26   3.655%   $201.3602   $201.36   $201.35   $201.40  
  7 purchase totals = $1,301.58       $1,416.7342   $1,416.72   $1,416.75   $1,416.80