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 $57.85   6.149%   $61.4072   $61.41   $61.40   $61.40  
  Purchase #2 $108.51   4.874%   $113.7988   $113.80   $113.80   $113.80  
  Purchase #3 $61.49   7.565%   $66.1417   $66.14   $66.15   $66.10  
  Purchase #4 $8.58   7.721%   $9.2425   $9.24   $9.25   $9.20  
  Purchase #5 $216.93   13.486%   $246.1852   $246.19   $246.20   $246.20  
  Purchase #6 $241.60   9.182%   $263.7837   $263.78   $263.80   $263.80  
  Purchase #7 $160.40   3.169%   $165.4831   $165.48   $165.50   $165.50  
  7 purchase totals = $855.36       $926.0422   $926.04   $926.10   $926.00