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 $86.27   13.682%   $98.0735   $98.07   $98.05   $98.10  
  Purchase #2 $59.98   3.516%   $62.0889   $62.09   $62.10   $62.10  
  Purchase #3 $11.38   12.568%   $12.8102   $12.81   $12.80   $12.80  
  Purchase #4 $188.33   5.295%   $198.3021   $198.30   $198.30   $198.30  
  Purchase #5 $217.40   13.433%   $246.6033   $246.60   $246.60   $246.60  
  Purchase #6 $23.37   6.359%   $24.8561   $24.86   $24.85   $24.90  
  Purchase #7 $233.54   5.426%   $246.2119   $246.21   $246.20   $246.20  
  7 purchase totals = $820.27       $888.9460   $888.94   $888.90   $889.00