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 $102.82   13.398%   $116.5958   $116.60   $116.60   $116.60  
  Purchase #2 $94.84   3.219%   $97.8929   $97.89   $97.90   $97.90  
  Purchase #3 $203.40   10.234%   $224.216   $224.22   $224.20   $224.20  
  Purchase #4 $86.82   7.415%   $93.2577   $93.26   $93.25   $93.30  
  Purchase #5 $180.50   11.770%   $201.7449   $201.74   $201.75   $201.70  
  Purchase #6 $37.43   7.500%   $40.2373   $40.24   $40.25   $40.20  
  Purchase #7 $114.63   4.408%   $119.6829   $119.68   $119.70   $119.70  
  7 purchase totals = $820.44       $893.6275   $893.63   $893.65   $893.60