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 $156.62   8.288%   $169.6007   $169.60   $169.60   $169.60  
  Purchase #2 $241.75   4.295%   $252.1332   $252.13   $252.15   $252.10  
  Purchase #3 $127.64   10.395%   $140.9082   $140.91   $140.90   $140.90  
  Purchase #4 $160.28   3.819%   $166.4011   $166.40   $166.40   $166.40  
  Purchase #5 $180.73   6.767%   $192.96   $192.96   $192.95   $193.00  
  Purchase #6 $194.29   8.643%   $211.0825   $211.08   $211.10   $211.10  
  Purchase #7 $221.64   5.806%   $234.5084   $234.51   $234.50   $234.50  
  7 purchase totals = $1,282.95       $1,367.5941   $1,367.59   $1,367.60   $1,367.60