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 $232.91   10.640%   $257.6916   $257.69   $257.70   $257.70  
  Purchase #2 $174.50   5.653%   $184.3645   $184.36   $184.35   $184.40  
  Purchase #3 $159.49   11.477%   $177.7947   $177.79   $177.80   $177.80  
  Purchase #4 $247.29   5.147%   $260.018   $260.02   $260.00   $260.00  
  Purchase #5 $234.41   7.799%   $252.6916   $252.69   $252.70   $252.70  
  Purchase #6 $117.41   13.175%   $132.8788   $132.88   $132.90   $132.90  
  Purchase #7 $247.57   12.847%   $279.3753   $279.38   $279.40   $279.40  
  7 purchase totals = $1,413.58       $1,544.8145   $1,544.81   $1,544.85   $1,544.90