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 $95.66   6.129%   $101.523   $101.52   $101.50   $101.50  
  Purchase #2 $29.35   8.253%   $31.7723   $31.77   $31.75   $31.80  
  Purchase #3 $111.61   9.833%   $122.5846   $122.58   $122.60   $122.60  
  Purchase #4 $126.55   3.385%   $130.8337   $130.83   $130.85   $130.80  
  Purchase #5 $78.73   12.197%   $88.3327   $88.33   $88.35   $88.30  
  Purchase #6 $229.43   5.491%   $242.028   $242.03   $242.05   $242.00  
  Purchase #7 $114.51   13.497%   $129.9654   $129.97   $129.95   $130.00  
  7 purchase totals = $785.84       $847.0397   $847.03   $847.05   $847.00