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 $74.74   13.469%   $84.8067   $84.81   $84.80   $84.80  
  Purchase #2 $73.71   10.263%   $81.2749   $81.27   $81.25   $81.30  
  Purchase #3 $5.48   4.380%   $5.72   $5.72   $5.70   $5.70  
  Purchase #4 $158.60   5.617%   $167.5086   $167.51   $167.50   $167.50  
  Purchase #5 $244.79   12.473%   $275.3227   $275.32   $275.30   $275.30  
  Purchase #6 $207.86   6.125%   $220.5914   $220.59   $220.60   $220.60  
  Purchase #7 $168.82   11.850%   $188.8252   $188.83   $188.85   $188.80  
  7 purchase totals = $934.00       $1,024.0495   $1,024.05   $1,024.00   $1,024.00