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 $162.87   8.331%   $176.4387   $176.44   $176.45   $176.40  
  Purchase #2 $117.77   12.315%   $132.2734   $132.27   $132.25   $132.30  
  Purchase #3 $241.55   11.362%   $268.9949   $268.99   $269.00   $269.00  
  Purchase #4 $57.29   7.792%   $61.754   $61.75   $61.75   $61.80  
  Purchase #5 $52.96   3.761%   $54.9518   $54.95   $54.95   $55.00  
  Purchase #6 $5.30   10.536%   $5.8584   $5.86   $5.85   $5.90  
  Purchase #7 $37.36   3.608%   $38.7079   $38.71   $38.70   $38.70  
  7 purchase totals = $675.10       $738.9791   $738.97   $738.95   $739.10