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 $242.86   10.330%   $267.9474   $267.95   $267.95   $267.90  
  Purchase #2 $44.62   4.766%   $46.7466   $46.75   $46.75   $46.70  
  Purchase #3 $41.62   4.702%   $43.577   $43.58   $43.60   $43.60  
  Purchase #4 $74.91   7.483%   $80.5155   $80.52   $80.50   $80.50  
  Purchase #5 $18.39   11.287%   $20.4657   $20.47   $20.45   $20.50  
  Purchase #6 $31.26   9.680%   $34.286   $34.29   $34.30   $34.30  
  Purchase #7 $30.51   9.143%   $33.2995   $33.30   $33.30   $33.30  
  7 purchase totals = $484.17       $526.8377   $526.86   $526.85   $526.80