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 $33.96   3.174%   $35.0379   $35.04   $35.05   $35.00  
  Purchase #2 $156.90   5.227%   $165.1012   $165.10   $165.10   $165.10  
  Purchase #3 $113.45   10.343%   $125.1841   $125.18   $125.20   $125.20  
  Purchase #4 $187.36   11.201%   $208.3462   $208.35   $208.35   $208.30  
  Purchase #5 $73.32   6.123%   $77.8094   $77.81   $77.80   $77.80  
  Purchase #6 $216.79   5.552%   $228.8262   $228.83   $228.85   $228.80  
  Purchase #7 $74.89   9.510%   $82.012   $82.01   $82.00   $82.00  
  7 purchase totals = $856.67       $922.3170   $922.32   $922.35   $922.20