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 $243.27   11.669%   $271.6572   $271.66   $271.65   $271.70  
  Purchase #2 $181.75   3.275%   $187.7023   $187.70   $187.70   $187.70  
  Purchase #3 $178.40   7.620%   $191.9941   $191.99   $192.00   $192.00  
  Purchase #4 $23.32   7.581%   $25.0879   $25.09   $25.10   $25.10  
  Purchase #5 $47.29   6.180%   $50.2125   $50.21   $50.20   $50.20  
  Purchase #6 $236.45   3.616%   $245   $245.00   $245.00   $245.00  
  Purchase #7 $147.70   5.339%   $155.5857   $155.59   $155.60   $155.60  
  7 purchase totals = $1,058.18       $1,127.2397   $1,127.24   $1,127.25   $1,127.30