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 $246.30   7.585%   $264.9819   $264.98   $265.00   $265.00  
  Purchase #2 $156.59   12.157%   $175.6266   $175.63   $175.65   $175.60  
  Purchase #3 $86.85   4.497%   $90.7556   $90.76   $90.75   $90.80  
  Purchase #4 $223.75   6.638%   $238.6025   $238.60   $238.60   $238.60  
  Purchase #5 $24.70   9.850%   $27.133   $27.13   $27.15   $27.10  
  Purchase #6 $164.33   5.868%   $173.9729   $173.97   $173.95   $174.00  
  Purchase #7 $32.80   8.440%   $35.5683   $35.57   $35.55   $35.60  
  7 purchase totals = $935.32       $1,006.6408   $1,006.64   $1,006.65   $1,006.70