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 $242.47   10.500%   $267.9294   $267.93   $267.95   $267.90  
  Purchase #2 $247.46   11.319%   $275.47   $275.47   $275.45   $275.50  
  Purchase #3 $183.37   5.377%   $193.2298   $193.23   $193.25   $193.20  
  Purchase #4 $33.52   12.282%   $37.6369   $37.64   $37.65   $37.60  
  Purchase #5 $119.45   4.530%   $124.8611   $124.86   $124.85   $124.90  
  Purchase #6 $248.51   3.847%   $258.0702   $258.07   $258.05   $258.10  
  Purchase #7 $34.32   10.759%   $38.0125   $38.01   $38.00   $38.00  
  7 purchase totals = $1,109.10       $1,195.2099   $1,195.21   $1,195.20   $1,195.20