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 $195.81   12.111%   $219.5245   $219.52   $219.50   $219.50  
  Purchase #2 $229.35   5.494%   $241.9505   $241.95   $241.95   $242.00  
  Purchase #3 $58.91   4.224%   $61.3984   $61.40   $61.40   $61.40  
  Purchase #4 $196.44   6.416%   $209.0436   $209.04   $209.05   $209.00  
  Purchase #5 $66.43   11.577%   $74.1206   $74.12   $74.10   $74.10  
  Purchase #6 $72.26   5.154%   $75.9843   $75.98   $76.00   $76.00  
  Purchase #7 $153.43   5.529%   $161.9131   $161.91   $161.90   $161.90  
  7 purchase totals = $972.63       $1,043.9350   $1,043.92   $1,043.90   $1,043.90