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 $250.84   10.237%   $276.5185   $276.52   $276.50   $276.50  
  Purchase #2 $85.42   9.604%   $93.6237   $93.62   $93.60   $93.60  
  Purchase #3 $41.39   6.173%   $43.945   $43.95   $43.95   $43.90  
  Purchase #4 $98.58   5.577%   $104.0778   $104.08   $104.10   $104.10  
  Purchase #5 $196.53   13.594%   $223.2463   $223.25   $223.25   $223.20  
  Purchase #6 $157.88   10.743%   $174.841   $174.84   $174.85   $174.80  
  Purchase #7 $54.26   7.606%   $58.387   $58.39   $58.40   $58.40  
  7 purchase totals = $884.90       $974.6393   $974.65   $974.65   $974.50