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 $218.52   12.607%   $246.0688   $246.07   $246.05   $246.10  
  Purchase #2 $131.57   5.333%   $138.5866   $138.59   $138.60   $138.60  
  Purchase #3 $43.71   4.706%   $45.767   $45.77   $45.75   $45.80  
  Purchase #4 $118.58   10.422%   $130.9384   $130.94   $130.95   $130.90  
  Purchase #5 $67.63   10.516%   $74.742   $74.74   $74.75   $74.70  
  Purchase #6 $111.33   11.319%   $123.9314   $123.93   $123.95   $123.90  
  Purchase #7 $195.74   6.788%   $209.0268   $209.03   $209.05   $209.00  
  7 purchase totals = $887.08       $969.0610   $969.07   $969.10   $969.00