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 $238.38   13.235%   $269.9296   $269.93   $269.95   $269.90  
  Purchase #2 $214.58   7.348%   $230.3473   $230.35   $230.35   $230.30  
  Purchase #3 $84.48   13.134%   $95.5756   $95.58   $95.60   $95.60  
  Purchase #4 $147.62   5.768%   $156.1347   $156.13   $156.15   $156.10  
  Purchase #5 $184.97   10.659%   $204.686   $204.69   $204.70   $204.70  
  Purchase #6 $33.95   3.427%   $35.1135   $35.11   $35.10   $35.10  
  Purchase #7 $213.48   9.777%   $234.3519   $234.35   $234.35   $234.40  
  7 purchase totals = $1,117.46       $1,226.1386   $1,226.14   $1,226.20   $1,226.10