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 $56.30   8.596%   $61.1395   $61.14   $61.15   $61.10  
  Purchase #2 $210.77   5.362%   $222.0715   $222.07   $222.05   $222.10  
  Purchase #3 $10.87   3.654%   $11.2672   $11.27   $11.25   $11.30  
  Purchase #4 $226.66   3.691%   $235.026   $235.03   $235.05   $235.00  
  Purchase #5 $149.80   11.639%   $167.2352   $167.24   $167.25   $167.20  
  Purchase #6 $211.36   10.144%   $232.8004   $232.80   $232.80   $232.80  
  Purchase #7 $18.80   3.571%   $19.4713   $19.47   $19.45   $19.50  
  7 purchase totals = $884.56       $949.0111   $949.02   $949.00   $949.00