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 $56.93   8.150%   $61.5698   $61.57   $61.55   $61.60  
  Purchase #2 $204.34   6.783%   $218.2004   $218.20   $218.20   $218.20  
  Purchase #3 $237.63   5.523%   $250.7543   $250.75   $250.75   $250.80  
  Purchase #4 $86.92   9.299%   $95.0027   $95.00   $95.00   $95.00  
  Purchase #5 $26.62   4.193%   $27.7362   $27.74   $27.75   $27.70  
  Purchase #6 $110.48   6.640%   $117.8159   $117.82   $117.80   $117.80  
  Purchase #7 $36.65   8.498%   $39.7645   $39.76   $39.75   $39.80  
  7 purchase totals = $759.57       $810.8438   $810.84   $810.80   $810.90