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 $248.32   11.110%   $275.9084   $275.91   $275.90   $275.90  
  Purchase #2 $69.53   5.187%   $73.1365   $73.14   $73.15   $73.10  
  Purchase #3 $32.27   13.446%   $36.609   $36.61   $36.60   $36.60  
  Purchase #4 $70.52   3.737%   $73.1553   $73.16   $73.15   $73.20  
  Purchase #5 $41.59   11.841%   $46.5147   $46.51   $46.50   $46.50  
  Purchase #6 $228.98   8.180%   $247.7106   $247.71   $247.70   $247.70  
  Purchase #7 $60.34   4.554%   $63.0879   $63.09   $63.10   $63.10  
  7 purchase totals = $751.55       $816.1224   $816.13   $816.10   $816.10