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 $63.81   8.109%   $68.9844   $68.98   $69.00   $69.00  
  Purchase #2 $24.78   4.735%   $25.9533   $25.95   $25.95   $26.00  
  Purchase #3 $126.46   9.202%   $138.0968   $138.10   $138.10   $138.10  
  Purchase #4 $247.77   8.775%   $269.5118   $269.51   $269.50   $269.50  
  Purchase #5 $209.38   11.619%   $233.7079   $233.71   $233.70   $233.70  
  Purchase #6 $163.30   11.369%   $181.8656   $181.87   $181.85   $181.90  
  Purchase #7 $53.97   8.324%   $58.4625   $58.46   $58.45   $58.50  
  7 purchase totals = $889.47       $976.5823   $976.58   $976.55   $976.70