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 $56.88   8.401%   $61.6585   $61.66   $61.65   $61.70  
  Purchase #2 $47.52   8.158%   $51.3967   $51.40   $51.40   $51.40  
  Purchase #3 $208.64   13.709%   $237.2425   $237.24   $237.25   $237.20  
  Purchase #4 $209.51   5.395%   $220.8131   $220.81   $220.80   $220.80  
  Purchase #5 $236.25   11.555%   $263.5487   $263.55   $263.55   $263.50  
  Purchase #6 $201.26   5.435%   $212.1985   $212.20   $212.20   $212.20  
  Purchase #7 $27.82   6.824%   $29.7184   $29.72   $29.70   $29.70  
  7 purchase totals = $987.88       $1,076.5764   $1,076.58   $1,076.55   $1,076.50