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 $76.98   8.853%   $83.795   $83.80   $83.80   $83.80  
  Purchase #2 $77.72   11.328%   $86.5241   $86.52   $86.50   $86.50  
  Purchase #3 $56.57   8.293%   $61.2614   $61.26   $61.25   $61.30  
  Purchase #4 $209.28   3.471%   $216.5441   $216.54   $216.55   $216.50  
  Purchase #5 $105.82   3.237%   $109.2454   $109.25   $109.25   $109.20  
  Purchase #6 $123.49   7.811%   $133.1358   $133.14   $133.15   $133.10  
  Purchase #7 $216.25   5.604%   $228.3687   $228.37   $228.35   $228.40  
  7 purchase totals = $866.11       $918.8745   $918.88   $918.85   $918.80