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 $211.68   6.779%   $226.0298   $226.03   $226.05   $226.00  
  Purchase #2 $127.41   10.560%   $140.8645   $140.86   $140.85   $140.90  
  Purchase #3 $241.80   11.417%   $269.4063   $269.41   $269.40   $269.40  
  Purchase #4 $116.98   6.277%   $124.3228   $124.32   $124.30   $124.30  
  Purchase #5 $53.74   11.413%   $59.8733   $59.87   $59.85   $59.90  
  Purchase #6 $119.79   5.613%   $126.5138   $126.51   $126.50   $126.50  
  Purchase #7 $33.47   4.445%   $34.9577   $34.96   $34.95   $35.00  
  7 purchase totals = $904.87       $981.9682   $981.96   $981.90   $982.00