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 $231.33   13.294%   $262.083   $262.08   $262.10   $262.10  
  Purchase #2 $247.53   13.454%   $280.8327   $280.83   $280.85   $280.80  
  Purchase #3 $114.38   11.683%   $127.743   $127.74   $127.75   $127.70  
  Purchase #4 $25.79   10.286%   $28.4428   $28.44   $28.45   $28.40  
  Purchase #5 $239.70   11.620%   $267.5531   $267.55   $267.55   $267.60  
  Purchase #6 $176.70   5.854%   $187.044   $187.04   $187.05   $187.00  
  Purchase #7 $51.60   10.210%   $56.8684   $56.87   $56.85   $56.90  
  7 purchase totals = $1,087.03       $1,210.5670   $1,210.55   $1,210.60   $1,210.50