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 $153.31   10.205%   $168.9553   $168.96   $168.95   $169.00  
  Purchase #2 $120.54   4.240%   $125.6509   $125.65   $125.65   $125.70  
  Purchase #3 $23.72   5.874%   $25.1133   $25.11   $25.10   $25.10  
  Purchase #4 $109.62   6.760%   $117.0303   $117.03   $117.05   $117.00  
  Purchase #5 $84.46   13.210%   $95.6172   $95.62   $95.60   $95.60  
  Purchase #6 $119.32   5.270%   $125.6082   $125.61   $125.60   $125.60  
  Purchase #7 $239.59   3.251%   $247.3791   $247.38   $247.40   $247.40  
  7 purchase totals = $850.56       $905.3543   $905.36   $905.35   $905.40