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 $56.61   11.242%   $62.9741   $62.97   $62.95   $63.00  
  Purchase #2 $154.98   13.419%   $175.7768   $175.78   $175.80   $175.80  
  Purchase #3 $38.56   13.408%   $43.7301   $43.73   $43.75   $43.70  
  Purchase #4 $217.75   9.292%   $237.9833   $237.98   $238.00   $238.00  
  Purchase #5 $56.28   9.160%   $61.4352   $61.44   $61.45   $61.40  
  Purchase #6 $120.32   3.450%   $124.471   $124.47   $124.45   $124.50  
  Purchase #7 $196.25   12.226%   $220.2435   $220.24   $220.25   $220.20  
  7 purchase totals = $840.75       $926.6140   $926.61   $926.65   $926.60