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 $53.88   13.170%   $60.976   $60.98   $61.00   $61.00  
  Purchase #2 $142.57   8.366%   $154.4974   $154.50   $154.50   $154.50  
  Purchase #3 $58.35   12.808%   $65.8235   $65.82   $65.80   $65.80  
  Purchase #4 $193.98   8.219%   $209.9232   $209.92   $209.90   $209.90  
  Purchase #5 $250.40   5.586%   $264.3873   $264.39   $264.40   $264.40  
  Purchase #6 $85.67   7.212%   $91.8485   $91.85   $91.85   $91.80  
  Purchase #7 $117.68   7.378%   $126.3624   $126.36   $126.35   $126.40  
  7 purchase totals = $902.53       $973.8183   $973.82   $973.80   $973.80