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 $250.48   10.113%   $275.811   $275.81   $275.80   $275.80  
  Purchase #2 $53.70   3.763%   $55.7207   $55.72   $55.70   $55.70  
  Purchase #3 $221.66   13.784%   $252.2136   $252.21   $252.20   $252.20  
  Purchase #4 $238.53   6.549%   $254.1513   $254.15   $254.15   $254.20  
  Purchase #5 $165.26   4.126%   $172.0786   $172.08   $172.10   $172.10  
  Purchase #6 $203.90   3.296%   $210.6205   $210.62   $210.60   $210.60  
  Purchase #7 $235.40   13.839%   $267.977   $267.98   $268.00   $268.00  
  7 purchase totals = $1,368.93       $1,488.5727   $1,488.57   $1,488.55   $1,488.60