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 $241.59   13.707%   $274.7047   $274.70   $274.70   $274.70  
  Purchase #2 $212.93   12.523%   $239.5952   $239.60   $239.60   $239.60  
  Purchase #3 $239.68   6.656%   $255.6331   $255.63   $255.65   $255.60  
  Purchase #4 $202.40   13.554%   $229.8333   $229.83   $229.85   $229.80  
  Purchase #5 $90.30   3.195%   $93.1851   $93.19   $93.20   $93.20  
  Purchase #6 $221.75   3.636%   $229.8128   $229.81   $229.80   $229.80  
  Purchase #7 $59.81   3.794%   $62.0792   $62.08   $62.10   $62.10  
  7 purchase totals = $1,268.46       $1,384.8434   $1,384.84   $1,384.90   $1,384.80