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 $48.90   9.123%   $53.3611   $53.36   $53.35   $53.40  
  Purchase #2 $60.79   11.847%   $67.9918   $67.99   $68.00   $68.00  
  Purchase #3 $56.72   12.257%   $63.6722   $63.67   $63.65   $63.70  
  Purchase #4 $46.37   7.598%   $49.8932   $49.89   $49.90   $49.90  
  Purchase #5 $78.69   12.861%   $88.8103   $88.81   $88.80   $88.80  
  Purchase #6 $111.77   11.816%   $124.9767   $124.98   $125.00   $125.00  
  Purchase #7 $14.59   4.485%   $15.2444   $15.24   $15.25   $15.20  
  7 purchase totals = $417.83       $463.9497   $463.94   $463.95   $464.00