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 $45.49   10.444%   $50.241   $50.24   $50.25   $50.20  
  Purchase #2 $201.72   10.797%   $223.4997   $223.50   $223.50   $223.50  
  Purchase #3 $6.58   7.854%   $7.0968   $7.10   $7.10   $7.10  
  Purchase #4 $188.62   3.257%   $194.7634   $194.76   $194.75   $194.80  
  Purchase #5 $178.86   12.323%   $200.9009   $200.90   $200.90   $200.90  
  Purchase #6 $170.26   10.854%   $188.74   $188.74   $188.75   $188.70  
  Purchase #7 $51.32   5.205%   $53.9912   $53.99   $54.00   $54.00  
  7 purchase totals = $842.85       $919.2330   $919.23   $919.25   $919.20