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 $59.94   11.588%   $66.8858   $66.89   $66.90   $66.90  
  Purchase #2 $161.71   10.659%   $178.9467   $178.95   $178.95   $178.90  
  Purchase #3 $198.42   10.383%   $219.0219   $219.02   $219.00   $219.00  
  Purchase #4 $141.69   7.610%   $152.4726   $152.47   $152.45   $152.50  
  Purchase #5 $177.31   13.365%   $201.0075   $201.01   $201.00   $201.00  
  Purchase #6 $142.99   6.408%   $152.1528   $152.15   $152.15   $152.20  
  Purchase #7 $26.75   4.847%   $28.0466   $28.05   $28.05   $28.00  
  7 purchase totals = $908.81       $998.5339   $998.54   $998.50   $998.50