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 $201.26   12.716%   $226.8522   $226.85   $226.85   $226.90  
  Purchase #2 $18.49   9.224%   $20.1955   $20.20   $20.20   $20.20  
  Purchase #3 $14.91   4.341%   $15.5572   $15.56   $15.55   $15.60  
  Purchase #4 $91.91   4.173%   $95.7454   $95.75   $95.75   $95.70  
  Purchase #5 $108.61   13.137%   $122.8781   $122.88   $122.90   $122.90  
  Purchase #6 $107.46   11.199%   $119.4944   $119.49   $119.50   $119.50  
  Purchase #7 $85.30   7.625%   $91.8041   $91.80   $91.80   $91.80  
  7 purchase totals = $627.94       $692.5269   $692.53   $692.55   $692.60