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 $238.26   5.872%   $252.2506   $252.25   $252.25   $252.30  
  Purchase #2 $228.95   4.391%   $239.0032   $239.00   $239.00   $239.00  
  Purchase #3 $35.32   4.250%   $36.8211   $36.82   $36.80   $36.80  
  Purchase #4 $155.40   13.226%   $175.9532   $175.95   $175.95   $176.00  
  Purchase #5 $215.94   12.538%   $243.0146   $243.01   $243.00   $243.00  
  Purchase #6 $228.28   6.244%   $242.5338   $242.53   $242.55   $242.50  
  Purchase #7 $230.64   5.164%   $242.5502   $242.55   $242.55   $242.60  
  7 purchase totals = $1,332.79       $1,432.1267   $1,432.11   $1,432.10   $1,432.20