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 $65.72   13.112%   $74.3372   $74.34   $74.35   $74.30  
  Purchase #2 $110.93   4.345%   $115.7499   $115.75   $115.75   $115.70  
  Purchase #3 $21.39   4.250%   $22.2991   $22.30   $22.30   $22.30  
  Purchase #4 $102.28   10.189%   $112.7013   $112.70   $112.70   $112.70  
  Purchase #5 $77.71   9.520%   $85.108   $85.11   $85.10   $85.10  
  Purchase #6 $154.68   11.102%   $171.8526   $171.85   $171.85   $171.90  
  Purchase #7 $246.74   5.300%   $259.8172   $259.82   $259.80   $259.80  
  7 purchase totals = $779.45       $841.8653   $841.87   $841.85   $841.80