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 $93.44   3.156%   $96.389   $96.39   $96.40   $96.40  
  Purchase #2 $24.32   12.664%   $27.3999   $27.40   $27.40   $27.40  
  Purchase #3 $117.47   12.587%   $132.2559   $132.26   $132.25   $132.30  
  Purchase #4 $144.28   6.738%   $154.0016   $154.00   $154.00   $154.00  
  Purchase #5 $193.76   3.868%   $201.2546   $201.25   $201.25   $201.30  
  Purchase #6 $180.63   8.372%   $195.7523   $195.75   $195.75   $195.80  
  Purchase #7 $234.67   12.295%   $263.5227   $263.52   $263.50   $263.50  
  7 purchase totals = $988.57       $1,070.5760   $1,070.57   $1,070.55   $1,070.70