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 $244.43   10.847%   $270.9433   $270.94   $270.95   $270.90  
  Purchase #2 $49.83   11.432%   $55.5266   $55.53   $55.55   $55.50  
  Purchase #3 $33.48   9.104%   $36.528   $36.53   $36.55   $36.50  
  Purchase #4 $61.34   3.274%   $63.3483   $63.35   $63.35   $63.30  
  Purchase #5 $25.51   4.273%   $26.6   $26.60   $26.60   $26.60  
  Purchase #6 $247.53   6.545%   $263.7308   $263.73   $263.75   $263.70  
  Purchase #7 $30.92   11.473%   $34.4675   $34.47   $34.45   $34.50  
  7 purchase totals = $693.04       $751.1445   $751.15   $751.20   $751.00