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 $94.47   13.214%   $106.9533   $106.95   $106.95   $107.00  
  Purchase #2 $39.44   8.612%   $42.8366   $42.84   $42.85   $42.80  
  Purchase #3 $67.75   13.428%   $76.8475   $76.85   $76.85   $76.80  
  Purchase #4 $24.59   8.502%   $26.6806   $26.68   $26.70   $26.70  
  Purchase #5 $237.82   8.677%   $258.4556   $258.46   $258.45   $258.50  
  Purchase #6 $62.97   7.220%   $67.5164   $67.52   $67.50   $67.50  
  Purchase #7 $122.90   4.764%   $128.755   $128.76   $128.75   $128.80  
  7 purchase totals = $649.94       $708.0450   $708.06   $708.05   $708.10