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 $221.66   8.863%   $241.3057   $241.31   $241.30   $241.30  
  Purchase #2 $166.45   11.118%   $184.9559   $184.96   $184.95   $185.00  
  Purchase #3 $231.71   6.764%   $247.3829   $247.38   $247.40   $247.40  
  Purchase #4 $124.34   5.773%   $131.5181   $131.52   $131.50   $131.50  
  Purchase #5 $150.41   7.838%   $162.1991   $162.20   $162.20   $162.20  
  Purchase #6 $11.70   7.284%   $12.5522   $12.55   $12.55   $12.60  
  Purchase #7 $32.30   6.314%   $34.3394   $34.34   $34.35   $34.30  
  7 purchase totals = $938.57       $1,014.2533   $1,014.26   $1,014.25   $1,014.30