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 $234.37   11.560%   $261.4632   $261.46   $261.45   $261.50  
  Purchase #2 $121.84   11.764%   $136.1733   $136.17   $136.15   $136.20  
  Purchase #3 $168.75   3.633%   $174.8807   $174.88   $174.90   $174.90  
  Purchase #4 $249.84   7.143%   $267.6861   $267.69   $267.70   $267.70  
  Purchase #5 $220.45   9.360%   $241.0841   $241.08   $241.10   $241.10  
  Purchase #6 $204.92   3.269%   $211.6188   $211.62   $211.60   $211.60  
  Purchase #7 $69.67   5.193%   $73.288   $73.29   $73.30   $73.30  
  7 purchase totals = $1,269.84       $1,366.1942   $1,366.19   $1,366.20   $1,366.30