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 $182.90   13.502%   $207.5952   $207.60   $207.60   $207.60  
  Purchase #2 $115.90   7.329%   $124.3943   $124.39   $124.40   $124.40  
  Purchase #3 $14.84   4.768%   $15.5476   $15.55   $15.55   $15.50  
  Purchase #4 $92.52   7.812%   $99.7477   $99.75   $99.75   $99.70  
  Purchase #5 $157.55   10.443%   $174.0029   $174.00   $174.00   $174.00  
  Purchase #6 $190.96   3.190%   $197.0516   $197.05   $197.05   $197.10  
  Purchase #7 $195.96   6.415%   $208.5308   $208.53   $208.55   $208.50  
  7 purchase totals = $950.63       $1,026.8701   $1,026.87   $1,026.90   $1,026.80