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 $68.90   12.134%   $77.2603   $77.26   $77.25   $77.30  
  Purchase #2 $165.78   6.291%   $176.2092   $176.21   $176.20   $176.20  
  Purchase #3 $12.68   5.735%   $13.4072   $13.41   $13.40   $13.40  
  Purchase #4 $138.27   13.379%   $156.7691   $156.77   $156.75   $156.80  
  Purchase #5 $167.55   5.802%   $177.2713   $177.27   $177.25   $177.30  
  Purchase #6 $230.31   6.151%   $244.4764   $244.48   $244.50   $244.50  
  Purchase #7 $248.62   13.388%   $281.9052   $281.91   $281.90   $281.90  
  7 purchase totals = $1,032.11       $1,127.2987   $1,127.31   $1,127.25   $1,127.40