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 $241.45   11.273%   $268.6687   $268.67   $268.65   $268.70  
  Purchase #2 $236.59   10.469%   $261.3586   $261.36   $261.35   $261.40  
  Purchase #3 $168.30   7.484%   $180.8956   $180.90   $180.90   $180.90  
  Purchase #4 $19.96   13.205%   $22.5957   $22.60   $22.60   $22.60  
  Purchase #5 $77.51   13.399%   $87.8956   $87.90   $87.90   $87.90  
  Purchase #6 $238.56   12.602%   $268.6233   $268.62   $268.60   $268.60  
  Purchase #7 $211.43   4.153%   $220.2107   $220.21   $220.20   $220.20  
  7 purchase totals = $1,193.80       $1,310.2482   $1,310.26   $1,310.20   $1,310.30