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 $101.51   5.660%   $107.2555   $107.26   $107.25   $107.30  
  Purchase #2 $55.58   5.169%   $58.4529   $58.45   $58.45   $58.50  
  Purchase #3 $27.50   8.858%   $29.936   $29.94   $29.95   $29.90  
  Purchase #4 $141.60   3.260%   $146.2162   $146.22   $146.20   $146.20  
  Purchase #5 $180.43   11.767%   $201.6612   $201.66   $201.65   $201.70  
  Purchase #6 $54.30   3.232%   $56.055   $56.06   $56.05   $56.10  
  Purchase #7 $250.69   13.249%   $283.9039   $283.90   $283.90   $283.90  
  7 purchase totals = $811.61       $883.4807   $883.49   $883.45   $883.60