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 $90.28   6.243%   $95.9162   $95.92   $95.90   $95.90  
  Purchase #2 $180.95   4.688%   $189.4329   $189.43   $189.45   $189.40  
  Purchase #3 $103.68   7.545%   $111.5027   $111.50   $111.50   $111.50  
  Purchase #4 $182.76   6.841%   $195.2626   $195.26   $195.25   $195.30  
  Purchase #5 $229.51   10.662%   $253.9804   $253.98   $254.00   $254.00  
  Purchase #6 $159.86   12.341%   $179.5883   $179.59   $179.60   $179.60  
  Purchase #7 $228.72   5.377%   $241.0183   $241.02   $241.00   $241.00  
  7 purchase totals = $1,175.76       $1,266.7014   $1,266.70   $1,266.70   $1,266.70