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 $24.85   6.161%   $26.381   $26.38   $26.40   $26.40  
  Purchase #2 $116.95   7.268%   $125.4499   $125.45   $125.45   $125.40  
  Purchase #3 $214.78   13.429%   $243.6228   $243.62   $243.60   $243.60  
  Purchase #4 $244.51   10.746%   $270.785   $270.79   $270.80   $270.80  
  Purchase #5 $145.45   4.424%   $151.8847   $151.88   $151.90   $151.90  
  Purchase #6 $156.55   7.686%   $168.5824   $168.58   $168.60   $168.60  
  Purchase #7 $45.40   10.315%   $50.083   $50.08   $50.10   $50.10  
  7 purchase totals = $948.49       $1,036.7888   $1,036.78   $1,036.85   $1,036.80