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 $14.71   11.171%   $16.3533   $16.35   $16.35   $16.40  
  Purchase #2 $219.66   8.542%   $238.4234   $238.42   $238.40   $238.40  
  Purchase #3 $61.60   5.591%   $65.0441   $65.04   $65.05   $65.00  
  Purchase #4 $229.66   12.791%   $259.0358   $259.04   $259.05   $259.00  
  Purchase #5 $162.45   13.779%   $184.834   $184.83   $184.85   $184.80  
  Purchase #6 $177.60   5.160%   $186.7642   $186.76   $186.75   $186.80  
  Purchase #7 $75.64   6.800%   $80.7835   $80.78   $80.80   $80.80  
  7 purchase totals = $941.32       $1,031.2383   $1,031.22   $1,031.25   $1,031.20