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 $229.71   5.698%   $242.7989   $242.80   $242.80   $242.80  
  Purchase #2 $169.44   13.520%   $192.3483   $192.35   $192.35   $192.30  
  Purchase #3 $109.70   11.787%   $122.6303   $122.63   $122.65   $122.60  
  Purchase #4 $85.51   6.278%   $90.8783   $90.88   $90.90   $90.90  
  Purchase #5 $97.49   11.369%   $108.5736   $108.57   $108.55   $108.60  
  Purchase #6 $197.39   6.216%   $209.6598   $209.66   $209.65   $209.70  
  Purchase #7 $69.82   3.182%   $72.0417   $72.04   $72.05   $72.00  
  7 purchase totals = $959.06       $1,038.9309   $1,038.93   $1,038.95   $1,038.90