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 $165.48   6.743%   $176.6383   $176.64   $176.65   $176.60  
  Purchase #2 $47.73   9.561%   $52.2935   $52.29   $52.30   $52.30  
  Purchase #3 $17.96   6.759%   $19.1739   $19.17   $19.15   $19.20  
  Purchase #4 $68.69   9.557%   $75.2547   $75.25   $75.25   $75.30  
  Purchase #5 $80.28   13.773%   $91.337   $91.34   $91.35   $91.30  
  Purchase #6 $143.63   6.454%   $152.8999   $152.90   $152.90   $152.90  
  Purchase #7 $230.46   5.821%   $243.8751   $243.88   $243.90   $243.90  
  7 purchase totals = $754.23       $811.4724   $811.47   $811.50   $811.50