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 $196.95   13.444%   $223.428   $223.43   $223.45   $223.40  
  Purchase #2 $89.84   4.463%   $93.8496   $93.85   $93.85   $93.80  
  Purchase #3 $176.96   9.610%   $193.9659   $193.97   $193.95   $194.00  
  Purchase #4 $201.36   8.291%   $218.0548   $218.05   $218.05   $218.10  
  Purchase #5 $64.43   6.856%   $68.8473   $68.85   $68.85   $68.80  
  Purchase #6 $182.58   3.559%   $189.078   $189.08   $189.10   $189.10  
  Purchase #7 $65.64   5.351%   $69.1524   $69.15   $69.15   $69.20  
  7 purchase totals = $977.76       $1,056.3760   $1,056.38   $1,056.40   $1,056.40