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 $57.54   6.814%   $61.4608   $61.46   $61.45   $61.50  
  Purchase #2 $107.91   8.287%   $116.8525   $116.85   $116.85   $116.90  
  Purchase #3 $72.43   6.104%   $76.8511   $76.85   $76.85   $76.90  
  Purchase #4 $124.70   7.587%   $134.161   $134.16   $134.15   $134.20  
  Purchase #5 $99.34   8.118%   $107.4044   $107.40   $107.40   $107.40  
  Purchase #6 $167.40   6.216%   $177.8056   $177.81   $177.80   $177.80  
  Purchase #7 $148.34   5.515%   $156.521   $156.52   $156.50   $156.50  
  7 purchase totals = $777.66       $831.0564   $831.05   $831.00   $831.20