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 $61.81   6.127%   $65.5971   $65.60   $65.60   $65.60  
  Purchase #2 $148.33   5.640%   $156.6958   $156.70   $156.70   $156.70  
  Purchase #3 $168.82   4.257%   $176.0067   $176.01   $176.00   $176.00  
  Purchase #4 $232.81   11.309%   $259.1385   $259.14   $259.15   $259.10  
  Purchase #5 $79.33   13.775%   $90.2577   $90.26   $90.25   $90.30  
  Purchase #6 $229.28   4.718%   $240.0974   $240.10   $240.10   $240.10  
  Purchase #7 $5.57   11.369%   $6.2033   $6.20   $6.20   $6.20  
  7 purchase totals = $925.95       $993.9965   $994.01   $994.00   $994.00