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 $244.75   12.654%   $275.7207   $275.72   $275.70   $275.70  
  Purchase #2 $166.96   8.296%   $180.811   $180.81   $180.80   $180.80  
  Purchase #3 $115.99   12.580%   $130.5815   $130.58   $130.60   $130.60  
  Purchase #4 $60.80   11.302%   $67.6716   $67.67   $67.65   $67.70  
  Purchase #5 $64.29   11.465%   $71.6608   $71.66   $71.65   $71.70  
  Purchase #6 $235.27   10.499%   $259.971   $259.97   $259.95   $260.00  
  Purchase #7 $23.92   12.292%   $26.8602   $26.86   $26.85   $26.90  
  7 purchase totals = $911.98       $1,013.2768   $1,013.27   $1,013.20   $1,013.40